Network Working Group S. Silverberg
Request for Comments: 2446 Microsoft
Category: Standards Track S. Mansour
Netscape
F. Dawson
Lotus
R. Hopson
ON Technologies
November 1998
iCalendar Transport-Independent Interoperability Protocol(iTIP)Scheduling Events, BusyTime, To-dos and Journal Entries
Status of this Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (1998). All Rights Reserved.
Abstract
This document specifies how calendaring systems use iCalendar objects
to interoperate with other calendar systems. It does so in a general
way so as to allow multiple methods of communication between systems.
Subsequent documents specify interoperable methods of communications
between systems that use this protocol.
The document outlines a model for calendar exchange that defines both
static and dynamic event, to-do, journal and free/busy objects.
Static objects are used to transmit information from one entity to
another without the expectation of continuity or referential
integrity with the original item. Dynamic objects are a superset of
static objects and will gracefully degrade to their static
counterparts for clients that only support static objects.
This document specifies an Internet protocol based on the iCalendar
object specification that provides scheduling interoperability
between different calendar systems. The Internet protocol is called
the "iCalendar Transport-Independent Interoperability Protocol
(iTIP)".
Silverberg, et. al. Standards Track [Page 1]

RFC 2446 iTIP November 19981 Introduction
This document specifies how calendaring systems use iCalendar objects
to interoperate with other calendar systems. In particular, it
specifies how to schedule events, to-dos, or daily journal entries.
It further specifies how to search for available busy time
information. It does so in a general way so as to allow multiple
methods of communication between systems. Subsequent documents
specify transport bindings between systems that use this protocol.
This protocol is based on messages sent from an originator to one or
more recipients. For certain types of messages, a recipient may
reply, in order to update their status and may also return
transaction/request status information. The protocol supports the
ability for the message originator to modify or cancel the original
message. The protocol also supports the ability for recipients to
suggest changes to the originator of a message. The elements of the
protocol also define the user roles for its transactions.
1.1 Formatting Conventions
In order to refer to elements of the calendaring and scheduling
model, core object or interoperability protocol defined in [iCAL] and
[iTIP] several formatting conventions have been utilized.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY" and "OPTIONAL" in this
document are to be interpreted as described in [RFC-2119].
Calendaring and scheduling roles are referred to in quoted-strings of
text with the first character of each word in upper case. For
example, "Organizer" refers to a role of a "Calendar User" (CU)
within the scheduling protocol defined by [iTIP]. Calendar components
defined by [iCAL] are referred to with capitalized, quoted-strings of
text. All calendar components start with the letter "V". For example,
"VEVENT" refers to the event calendar component, "VTODO" refers to
the to-do calendar component and "VJOURNAL" refers to the daily
journal calendar component. Scheduling methods defined by [iTIP] are
referred to with capitalized, quoted-strings of text. For example,
"REQUEST" refers to the method for requesting a scheduling calendar
component be created or modified, "REPLY" refers to the method a
recipient of a request uses to update their status with the
"Organizer" of the calendar component.
Properties defined by [iCAL] are referred to with capitalized,
quoted-strings of text, followed by the word "property". For example,
"ATTENDEE" property refers to the iCalendar property used to convey
the calendar address of a "Calendar User". Property parameters
Silverberg, et. al. Standards Track [Page 5]

RFC 2446 iTIP November 1998
defined by this memo are referred to with lower case, quoted-strings
of text, followed by the word "parameter". For example, "value"
parameter refers to the iCalendar property parameter used to override
the default data type for a property value. Enumerated values defined
by this memo are referred to with capitalized text, either alone or
followed by the word "value".
In tables, the quoted-string text is specified without quotes in
order to minimize the table length.
1.2 Related Documents
Implementers will need to be familiar with several other memos that,
along with this one, describe the Internet calendaring and scheduling
standards. This document, [iTIP], specifies an interoperability
protocol for scheduling between different implementations. The
related documents are:
[iCAL] - specifies the objects, data types, properties and
property parameters used in the protocols, along with the
methods for representing and encoding them;
[iMIP] specifies an Internet email binding for [iTIP].
This memo does not attempt to repeat the specification of concepts or
definitions from these other memos. Where possible, references are
made to the memo that provides for the specification of these
concepts or definitions.
1.3 ITIP Roles and Transactions
ITIP defines methods for exchanging [iCAL] objects for the purposes
of group calendaring and scheduling between "Calendar Users" (CUs).
CUs take on one of two roles in iTIP. The CU who initiates an
exchange takes on the role of "Organizer". For example, the CU who
proposes a group meeting is the "Organizer". The CUs asked to
participate in the group meeting by the "Organizer" take on the role
of "Attendee". Note that "role" is also a descriptive parameter to
the _ATTENDEE_ property. Its use is to convey descriptive context to
an "Attendee" such as "chair", "req-participant" or "non-participant"
and has nothing to do with the calendaring workflow.
Silverberg, et. al. Standards Track [Page 6]

RFC 2446 iTIP November 1998
The ITIP methods are listed below and their usage and semantics are
defined in section 3 of this document.
+================+==================================================+
| Method | Description |
|================+==================================================|
| PUBLISH | Used to publish a calendar entry to one or more |
| | Calendar Users. There is no interactivity |
| | between the publisher and any other calendar |
| | user. An example might include a baseball team |
| | publishing its schedule to the public. |
| | |
| REQUEST | Used to schedule a calendar entry with other |
| | Calendar Users. Requests are interactive in that |
| | they require the receiver to respond using |
| | the Reply methods. Meeting Requests, Busy |
| | Time requests and the assignment of VTODOs to |
| | other Calendar Users are all examples. |
| | Requests are also used by the "Organizer" to |
| | update the status of a calendar entry. |
| | |
| REPLY | A Reply is used in response to a Request to |
| | convey "Attendee" status to the "Organizer". |
| | Replies are commonly used to respond to meeting |
| | and task requests. |
| | |
| ADD | Add one or more instances to an existing |
| | VEVENT, VTODO, or VJOURNAL. |
| | |
| CANCEL | Cancel one or more instances of an existing |
| | VEVENT, VTODO, or VJOURNAL. |
| | |
| REFRESH | The Refresh method is used by an "Attendee" to |
| | request the latest version of a calendar entry. |
| | |
| COUNTER | The Counter method is used by an "Attendee" to |
| | negotiate a change in the calendar entry. |
| | Examples include the request to change a |
| | proposed Event time or change the due date for a |
| | VTODO. |
| | |
| DECLINE- | Used by the "Organizer" to decline the proposed |
| COUNTER | counter-proprosal. |
+================+==================================================+
Silverberg, et. al. Standards Track [Page 7]

RFC 2446 iTIP November 1998
Group scheduling in iTIP is accomplished using the set of "request"
and "response" methods described above. The following table shows the
methods broken down by who can send them.
+================+==================================================+
| Originator | Methods |
|================+==================================================|
| Organizer | PUBLISH, REQUEST, ADD, CANCEL, DECLINECOUNTER |
| | |
| Attendee | REPLY, REFRESH, COUNTER |
| | REQUEST only when delegating |
+================+==================================================+
Note that for some calendar component types, the allowable methods
are a subset of the above set.
2 Interoperability Models
There are two distinct protocols relevant to interoperability: an
"Application Protocol" and a "Transport Protocol". The Application
Protocol defines the content of the iCalendar objects sent between
sender and receiver to accomplish the scheduling transactions listed
above. The Transport Protocol defines how the iCalendar objects are
sent between the sender and receiver. This document focuses on the
Application Protocol. Binding documents such as [iMIP] focus on the
Transport Protocol.
The connection between Sender and Receiver in the diagram below
refers to the Application Protocol. The iCalendar objects passed from
the Sender to the Receiver are presented in Section 3, Application
Protocol Elements.
+----------+ +----------+
| | iTIP | |
| Sender |<-------------------->| Receiver |
| | | |
+----------+ +----------+
There are several variations of this diagram in which the Sender and
Receiver take on various roles of a "Calendar User Agent" (CUA) or a
"Calendar Service" (CS).
The architecture of iTIP is depicted in the diagram below. An
application written to this specification may work with bindings for
the store-and-forward transport, the real time transport, or both.
Also note that iTIP could be bound to other transports.
Silverberg, et. al. Standards Track [Page 8]

RFC 2446 iTIP November 1998
+------------------------------------------+
| iTIP |
+------------------------------------------+
|Real-time | Store-and-Fwd | Other |
|Transport | Transport | Transports... |
+------------------------------------------+
2.1 Application Protocol
In the iTIP model, a calendar entry is created and managed by an
"Organizer". The "Organizer" interacts with other CUs by sending one
or more of the iTIP messages listed above. "Attendees" use the
"REPLY" method to communicate their status. "Attendees" do not make
direct changes to the master calendar entry. They can, however, use
the "COUNTER" method to suggest changes to the "Organizer". In any
case, the "Organizer" has complete control over the master calendar
entry.
2.1.1 Calendar Entry State
There are two distinct states relevant to calendar entries: the
overall state of the entry and the state associated with an
"Attendee" to that entry.
The state of an entry is defined by the "STATUS" property and is
controlled by the "Organizer." There is no default value for the
"STATUS" property. The "Organizer" sets the "STATUS" property to the
appropriate value for each calendar entry.
The state of a particular "Attendee" relative to an entry is defined
by the "partstat" parameter in the "ATTENDEE" property for each
"Attendee". When an "Organizer" issues the initial entry, "Attendee"
status is unknown. The "Organizer" specifies this by setting the
"partstat" parameter to "NEEDS-ACTION". Each "Attendee" modifies
their "ATTENDEE" property "partstat" parameter to an appropriate
value as part of a "REPLY" message sent back to the "Organizer".
2.1.2 Delegation
Delegation is defined as the process by which an "Attendee" grants
another CU (or several CUs) the right to attend on their behalf. The
"Organizer" is made aware of this change because the delegating
"Attendee" informs the "Organizer". These steps are detailed in the
REQUEST method section.
Silverberg, et. al. Standards Track [Page 9]

RFC 2446 iTIP November 19982.1.3 Acting on Behalf of other Calendar Users
In many organizations one user will act on behalf of another to
organize and/or respond to meeting requests. ITIP provides two
mechanisms that support these activities.
First, the "Organizer" is treated as a special entity, separate from
"Attendees". All responses from "Attendees" flow to the "Organizer",
making it easy to separate a calendar user organizing a meeting from
calendar users attending the meeting. Additionally, iCalendar
provides descriptive roles for each "Attendee". For instance, a role
of "chair" may be ascribed to one or more "Attendees". The "chair"
and the "Organizer" may or may not be the same calendar user. This
maps well to scenarios where an assistant may manage meeting
logistics for another individual who chairs a meeting.
Second, a "sent-by" parameter may be specified in either the
"Organizer" or "Attendee" properties. When specified, the "sent-by"
parameter indicates that the responding CU acted on behalf of the
specified "Attendee" or "Organizer".
2.1.4 Component Revisions
The "SEQUENCE" property is used by the "Organizer" to indicate
revisions to the calendar component. The rules for incrementing the
"SEQUENCE" number are defined in [iCAL]. For clarity, these rules are
paraphrased here in terms of how they are applied in [iTIP]. For a
given "UID" in a calendar component:
. For the "PUBLISH" and "REQUEST" methods, the "SEQUENCE" property
value is incremented according to the rules defined in [iCAL].
. The "SEQUENCE" property value MUST be incremented each time the
"Organizer" uses the "ADD" or "CANCEL" methods.
. The "SEQUENCE" property value MUST NOT be incremented when using
"REPLY", "REFRESH", "COUNTER", "DECLINECOUNTER", or when sending a
delegation "REQUEST".
In some circumstances the "Organizer" may not have received responses
to the final revision sent out. In this situation, the "Organizer"
may wish to send an update "REQUEST", and set "RSVP=TRUE" for all
"Attendees", so that current responses can be collected.
Silverberg, et. al. Standards Track [Page 10]

RFC 2446 iTIP November 1998
The value of the "SEQUENCE" property contained in a response from an
"Attendee" may not always match the "Organizer's" revision.
Implementations may choose to have the CUA indicate to the CU that
the response is to an entry that has been revised and allow the CU to
decide whether or not to accept the response.
2.1.5 Message Sequencing
CUAs that handle the [iTIP] application protocol must often correlate
a component in a calendar store with a component received in the
[iTIP] message. For example, an event may be updated with a later
revision of the same event. To accomplish this, a CUA must correlate
the version of the event already in its calendar store with the
version sent in the [iTIP] message. In addition to this correlation,
there are several factors that can cause [iTIP] messages to arrive in
an unexpected order. That is, an "Organizer" could receive a reply
to an earlier revision of a component AFTER receiving a reply to a
later revision.
To maximize interoperability and to handle messages that arrive in an
unexpected order, use the following rules:
1. The primary key for referencing a particular iCalendar component
is the "UID" property value. To reference an instance of a
recurring component, the primary key is composed of the "UID" and
the "RECURRENCE-ID" properties.
2. The secondary key for referencing a component is the "SEQUENCE"
property value. For components where the "UID" is the same, the
component with the highest numeric value for the "SEQUENCE"
property obsoletes all other revisions of the component with
lower values.
3. "Attendees" send "REPLY" messages to the "Organizer". For
replies where the "UID" property value is the same, the value of
the "SEQUENCE" property indicates the revision of the component
to which the "Attendee" is replying. The reply with the highest
numeric value for the "SEQUENCE" property obsoletes all other
replies with lower values.
4. In situations where the "UID" and "SEQUENCE" properties match,
the "DTSTAMP" property is used as the tie-breaker. The component
with the latest "DTSTAMP" overrides all others. Similarly, for
"Attendee" responses where the "UID" property values match and
the "SEQUENCE" property values match, the response with the
latest "DTSTAMP" overrides all others.
Silverberg, et. al. Standards Track [Page 11]

RFC 2446 iTIP November 1998
Hence, CUAs must persist the following component properties: "UID",
"RECURRENCE-ID", "SEQUENCE", and "DTSTAMP". Furthermore, for each
"ATTENDEE" property of a component CUAs must persist the "SEQUENCE"
and "DTSTAMP" property values associated with the "Attendee's"
response.
3 Application Protocol Elements
ITIP messages are "text/calendar" MIME entities that contain
calendaring and scheduling information. The particular type of [iCAL]
message is referred to as the "method type". Each method type is
identified by a "METHOD" property specified as part of the
"text/calendar" content type. The table below shows various
combinations of calendar components and the method types that this
memo supports.
+=================================================+
| | VEVENT | VTODO | VJOURNAL | VFREEBUSY |
|=================================================|
|Publish | Yes | Yes | Yes | Yes |
|Request | Yes | Yes | No | Yes |
|Refresh | Yes | Yes | No | No |
|Cancel | Yes | Yes | Yes | No |
|Add | Yes | Yes | Yes | No |
|Reply | Yes | Yes | No | Yes |
|Counter | Yes | Yes | No | No |
|Decline- | | | | |
|Counter | Yes | Yes | No | No |
+=================================================+
Each method type is defined in terms of its associated components and
properties. Some components and properties are required, some are
optional and others are excluded. The restrictions are expressed in
this document using a simple "restriction table". The first column
indicates the name of a component or property. Properties of the
iCalendar object are not indented. Properties of a component are
indented. The second column contains "MUST" if the component or
property must be present, "MAY" if the component or property is
optional, and "NOT" if the component or property must not be present.
Entries in the second column sometimes contain comments for further
clarification.
Silverberg, et. al. Standards Track [Page 12]

RFC 2446 iTIP November 19983.1 Common Component Restriction Tables
The restriction table below applies to properties of the iCalendar
object. That is, the properties at the outermost scope. The presence
column uses the following values to assert whether a property is
required, is optional and the number of times it may appear in the
iCalendar object.
Presence Value Description
--------------------------------------------------------------
1 One instance MUST be present
1+ At least one instance MUST be present
0 Instances of this property Must NOT be present
0+ Multiple instances MAY be present
0 or 1 Up to 1 instance of this property MAY be present
---------------------------------------------------------------
The tables also call out "X-PROPERTY" and "X-COMPONENT" to show
where vendor-specific properties and components can appear. The
tables do not lay out the restrictions of property parameters. Those
restrictions are defined in [iCAL].
Component/Property Presence
------------------- ----------------------------------------------
CALSCALE 0 or 1
PRODID 1
VERSION 1 Value MUST be "2.0"
X-PROPERTY 0+
DateTime values MAY refer to a "VTIMEZONE" component. The property
restrictions in the table below apply to any "VTIMEZONE" component in
an ITIP message.
Component/Property Presence
------------------- ----------------------------------------------
VTIMEZONE 0+ MUST be present if any date/time refers
to timezone
DAYLIGHT 0+ MUST be one or more of either STANDARD or
DAYLIGHT
COMMENT 0 or 1
DTSTART 1 MUST be local time format
RDATE 0+ if present RRULE MUST NOT be present
RRULE 0+ if present RDATE MUST NOT be present
TZNAME 0 or 1
TZOFFSET 1
TZOFFSETFROM 1
TZOFFSETTO 1
Silverberg, et. al. Standards Track [Page 13]

RFC 2446 iTIP November 1998
X-PROPERTY 0+
LAST-MODIFIED 0 or 1
STANDARD 0+ MUST be one or more of either STANDARD or
DAYLIGHT
COMMENT 0 or 1
DTSTART 1 MUST be local time format
RDATE 0+ if present RRULE MUST NOT be present
RRULE 0+ if present RDATE MUST NOT be present
TZNAME 0 or 1
TZOFFSETFROM 1
TZOFFSETTO 1
X-PROPERTY 0+
TZID 1
TZURL 0 or 1
X-PROPERTY 0+
The property restrictions in the table below apply to any "VALARM"
component in an ITIP message.
Component/Property Presence
------------------- ----------------------------------------------
VALARM 0+
ACTION 1
ATTACH 0+
DESCRIPTION 0 or 1
DURATION 0 or 1 if present REPEAT MUST be present
REPEAT 0 or 1 if present DURATION MUST be present
SUMMARY 0 or 1
TRIGGER 1
X-PROPERTY 0+
3.2 Methods for VEVENT Calendar Components
This section defines the property set restrictions for the method
types that are applicable to the "VEVENT" calendar component. Each
method is defined using a table that clarifies the property
constraints that define the particular method.
Silverberg, et. al. Standards Track [Page 14]

RFC 2446 iTIP November 1998
The following summarizes the methods that are defined for the
"VEVENT" calendar component.
+================+==================================================+
| Method | Description |
|================+==================================================|
| PUBLISH | Post notification of an event. Used primarily as |
| | a method of advertising the existence of an |
| | event. |
| | |
| REQUEST | Make a request for an event. This is an explicit |
| | invitation to one or more "Attendees". Event |
| | Requests are also used to update or change an |
| | existing event. Clients that cannot handle |
| | REQUEST may degrade the event to view it as an |
| | PUBLISH. |
| | |
| REPLY | Reply to an event request. Clients may set their |
| | status ("partstat") to ACCEPTED, DECLINED, |
| | TENTATIVE, or DELEGATED. |
| | |
| ADD | Add one or more instances to an existing event. |
| | |
| CANCEL | Cancel one or more instances of an existing |
| | event. |
| | |
| REFRESH | A request is sent to an "Organizer" by an |
| | "Attendee" asking for the latest version of an |
| | event to be resent to the requester. |
| | |
| COUNTER | Counter a REQUEST with an alternative proposal, |
| | Sent by an "Attendee" to the "Organizer". |
| | |
| DECLINECOUNTER | Decline a counter proposal. Sent to an |
| | "Attendee" by the "Organizer". |
+================+==================================================+
3.2.1 PUBLISH
The "PUBLISH" method in a "VEVENT" calendar component is an
unsolicited posting of an iCalendar object. Any CU may add published
components to their calendar. The "Organizer" MUST be present in a
published iCalendar component. "Attendees" MUST NOT be present. Its
expected usage is for encapsulating an arbitrary event as an
iCalendar object. The "Organizer" may subsequently update (with
another "PUBLISH" method), add instances to (with an "ADD" method),
or cancel (with a "CANCEL" method) a previously published "VEVENT"
calendar component.
Silverberg, et. al. Standards Track [Page 15]

RFC 2446 iTIP November 1998
This method type is an iCalendar object that conforms to the
following property constraints:
Component/Property Presence
------------------- ----------------------------------------------
METHOD 1 MUST equal "PUBLISH"
VEVENT 1+
DTSTAMP 1
DTSTART 1
ORGANIZER 1
SUMMARY 1 Can be null.
UID 1
RECURRENCE-ID 0 or 1 only if referring to an instance of a
recurring calendar component. Otherwise
it MUST NOT be present.
SEQUENCE 0 or 1 MUST be present if value is greater than
0, MAY be present if 0
ATTACH 0+
CATEGORIES 0 or 1 This property may contain a list of
values
CLASS 0 or 1
COMMENT 0 or 1
CONTACT 0+
CREATED 0 or 1
DESCRIPTION 0 or 1 Can be null
DTEND 0 or 1 if present DURATION MUST NOT be present
DURATION 0 or 1 if present DTEND MUST NOT be present
EXDATE 0+
EXRULE 0+
GEO 0 or 1
LAST-MODIFIED 0 or 1
LOCATION 0 or 1
PRIORITY 0 or 1
RDATE 0+
RELATED-TO 0+
RESOURCES 0 or 1 This property MAY contain a list of values
RRULE 0+
STATUS 0 or 1 MAY be one of TENTATIVE/CONFIRMED/CANCELLED
TRANSP 0 or 1
URL 0 or 1
X-PROPERTY 0+
ATTENDEE 0
REQUEST-STATUS 0
VALARM 0+
VFREEBUSY 0
VJOURNAL 0
Silverberg, et. al. Standards Track [Page 16]

RFC 2446 iTIP November 1998
VTODO 0
VTIMEZONE 0+ MUST be present if any date/time refers to
a timezone
X-COMPONENT 0+
3.2.2 REQUEST
The "REQUEST" method in a "VEVENT" component provides the following
scheduling functions:
. Invite "Attendees" to an event;
. Reschedule an existing event;
. Response to a REFRESH request;
. Update the details of an existing event, without rescheduling it;
. Update the status of "Attendees" of an existing event, without
rescheduling it;
. Reconfirm an existing event, without rescheduling it;
. Forward a "VEVENT" to another uninvited CU.
. For an existing "VEVENT" calendar component, delegate the role of
"Attendee" to another CU;
. For an existing "VEVENT" calendar component, changing the role of
"Organizer" to another CU.
The "Organizer" originates the "REQUEST". The recipients of the
"REQUEST" method are the CUs invited to the event, the "Attendees".
"Attendees" use the "REPLY" method to convey attendance status to the
"Organizer".
The "UID" and "SEQUENCE" properties are used to distinguish the
various uses of the "REQUEST" method. If the "UID" property value in
the "REQUEST" is not found on the recipient's calendar, then the
"REQUEST" is for a new "VEVENT" calendar component. If the "UID"
property value is found on the recipient's calendar, then the
"REQUEST" is for a rescheduling, an update, or a reconfirm of the
"VEVENT" calendar component.
For the "REQUEST" method, multiple "VEVENT" components in a single
iCalendar object are only permitted when for components with the same
"UID" property. That is, a series of recurring events may have
instance-specific information. In this case, multiple "VEVENT"
components are needed to express the entire series.
Silverberg, et. al. Standards Track [Page 17]

RFC 2446 iTIP November 1998
This method type is an iCalendar object that conforms to the
following property constraints:
Component/Property Presence
-----------------------------------------------------------------
METHOD 1 MUST be "REQUEST"
VEVENT 1+ All components MUST have the same UID
ATTENDEE 1+
DTSTAMP 1
DTSTART 1
ORGANIZER 1
SEQUENCE 0 or 1 MUST be present if value is greater than 0,
MAY be present if 0
SUMMARY 1 Can be null
UID 1
ATTACH 0+
CATEGORIES 0 or 1 This property may contain a list of values
CLASS 0 or 1
COMMENT 0 or 1
CONTACT 0+
CREATED 0 or 1
DESCRIPTION 0 or 1 Can be null
DTEND 0 or 1 if present DURATION MUST NOT be present
DURATION 0 or 1 if present DTEND MUST NOT be present
EXDATE 0+
EXRULE 0+
GEO 0 or 1
LAST-MODIFIED 0 or 1
LOCATION 0 or 1
PRIORITY 0 or 1
RDATE 0+
RECURRENCE-ID 0 or 1 only if referring to an instance of a
recurring calendar component. Otherwise it
MUST NOT be present.
RELATED-TO 0+
REQUEST-STATUS 0+
RESOURCES 0 or 1 This property MAY contain a list of values
RRULE 0+
STATUS 0 or 1 MAY be one of TENTATIVE/CONFIRMED
TRANSP 0 or 1
URL 0 or 1
X-PROPERTY 0+
VALARM 0+
VTIMEZONE 0+ MUST be present if any date/time refers to
a timezone
X-COMPONENT 0+
Silverberg, et. al. Standards Track [Page 18]

RFC 2446 iTIP November 1998
VFREEBUSY 0
VJOURNAL 0
VTODO 0
3.2.2.1 Rescheduling an Event
The "REQUEST" method may be used to reschedule an event. A
rescheduled event involves a change to the existing event in terms of
its time or recurrence intervals and possibly the location or
description. If the recipient CUA of a "REQUEST" method finds that
the "UID" property value already exists on the calendar, but that the
"SEQUENCE" (or "DTSTAMP") property value in the "REQUEST" method is
greater than the value for the existing event, then the "REQUEST"
method describes a rescheduling of the event.
3.2.2.2 Updating or Reconfirmation of an Event
The "REQUEST" method may be used to update or reconfirm an event. An
update to an existing event does not involve changes to the time or
recurrence intervals, and might not involve a change to the location
or description for the event. If the recipient CUA of a "REQUEST"
method finds that the "UID" property value already exists on the
calendar and that the "SEQUENCE" property value in the "REQUEST" is
the same as the value for the existing event, then the "REQUEST"
method describes an update of the event details, but no rescheduling
of the event.
The update "REQUEST" method is the appropriate response to a
"REFRESH" method sent from an "Attendee" to the "Organizer" of an
event.
The "Organizer" of an event may also send unsolicited "REQUEST"
methods. The unsolicited "REQUEST" methods may be used to update the
details of the event without rescheduling it, to update the
"partstat" parameter of "Attendees", or to reconfirm the event.
3.2.2.3 Delegating an Event to another CU
Some calendar and scheduling systems allow "Attendees" to delegate
their presence at an event to another calendar user. ITIP supports
this concept using the following workflow. Any "Attendee" may
delegate their right to participate in a calendar VEVENT to another
CU. The implication is that the delegate participates in lieu of the
original "Attendee"; NOT in addition to the "Attendee". The delegator
MUST notify the "Organizer" of this action using the steps outlined
below. Implementations may support or restrict delegation as they
see fit. For instance, some implementations may restrict a delegate
from delegating a "REQUEST" to another CU.
Silverberg, et. al. Standards Track [Page 19]

RFC 2446 iTIP November 1998
The "Delegator" of an event forwards the existing "REQUEST" to the
"Delegate". The "REQUEST" method MUST include an "ATTENDEE" property
with the calendar address of the "Delegate". The "Delegator" MUST
also send a "REPLY" method to the "Organizer" with the "Delegator's"
"ATTENDEE" property "partstat" parameter value set to "delegated". In
addition, the "delegated-to" parameter MUST be included with the
calendar address of the "Delegate".
In response to the request, the "Delegate" MUST send a "REPLY" method
to the "Organizer" and optionally, to the "Delegator". The "REPLY"
method " SHOULD include the "ATTENDEE" property with the "delegated-
from" parameter value of the "Delegator's" calendar address.
The "Delegator" may continue to receive updates to the event even
though they will not be attending. This is accomplished by the
"Delegator" setting their "role" attribute to " NON-PARTICIPANT" in
the "REPLY" to the "Organizer"
3.2.2.4 Changing the Organizer
The situation may arise where the "Organizer" of a VEVENT is no
longer able to perform the "Organizer" role and abdicates without
passing on the "Organizer" role to someone else. When this occurs the
"Attendees" of the VEVENT may use out-of-band mechanisms to
communicate the situation and agree upon a new "Organizer". The new
"Organizer" should then send out a new "REQUEST" with a modified
version of the VEVENT in which the "SEQUENCE" number has been
incremented and value of the "ORGANIZER" property has been changed to
the calendar address of the new "Organizer".
3.2.2.5 Sending on Behalf of the Organizer
There are a number of scenarios that support the need for a calendar
user to act on behalf of the "Organizer" without explicit role
changing. This might be the case if the CU designated as "Organizer"
was sick or unable to perform duties associated with that function.
In these cases iTIP supports the notion of one CU acting on behalf of
another. Using the "sent-by" parameter, a calendar user could send an
updated "VEVENT" REQUEST. In the case where one CU sends on behalf of
another CU, the "Attendee" responses are still directed back towards
the CU designated as "Organizer".
3.2.2.6 Forwarding to An Uninvited CU
An "Attendee" invited to an event may invite another uninvited CU to
the event. The invited "Attendee" accomplishes this by forwarding the
original "REQUEST" method to the uninvited CU. The "Organizer"
decides whether or not the uninvited CU is added to the attendee
Silverberg, et. al. Standards Track [Page 20]

RFC 2446 iTIP November 1998
list. If the "Organizer" decides not to add the uninvited CU no
further action is required, however the "Organizer" MAY send the
uninvited CU a "CANCEL" message. If the "Organizer" decides to add
an uninvited CU, a new "ATTENDEE" property is added for the uninvited
CU with its property parameters set as the "Organizer" deems
appropriate. When forwarding a "REQUEST" to another CU, the
forwarding "Attendee" MUST NOT make changes to the VEVENT property
set.
3.2.2.7 Updating Attendee Status
The "Organizer" of an event may also request updated status from one
or more "Attendees. The "Organizer" sends a "REQUEST" method to the
"Attendee" and sets the "ATTENDEE;RSVP=TRUE" property parameter. The
"SEQUENCE" property for the event is not changed from its previous
value. A recipient will determine that the only change in the
"REQUEST" is that their "RSVP" property parameter indicates a request
for updated status. The recipient SHOULD respond with a "REPLY"
method indicating their current status with respect to the "REQUEST".
3.2.3 REPLY
The "REPLY" method in a "VEVENT" calendar component is used to
respond (e.g., accept or decline) to a "REQUEST" or to reply to a
delegation "REQUEST". When used to provide a delegation response, the
"Delegator" SHOULD include the calendar address of the "Delegate" on
the "delegated-to" property parameter of the "Delegator's" "ATTENDEE"
property. The "Delegate" SHOULD include the calendar address of the
"Delegator" on the "delegated-from" property parameter of the
"Delegate's" "ATTENDEE" property.
The "REPLY" method may also be used to respond to an unsuccessful
"REQUEST" method. Depending on the value of the "REQUEST-STATUS"
property no scheduling action may have been performed.
The "Organizer" of an event may receive the "REPLY" method from a CU
not in the original "REQUEST". For example, a "REPLY" may be received
from a "Delegate" to an event. In addition, the "REPLY" method may be
received from an unknown CU (a "Party Crasher"). This uninvited
"Attendee" may be accepted, or the "Organizer" may cancel the event
for the uninvited "Attendee" by sending a "CANCEL" method to the
uninvited "Attendee".
An "Attendee" can include a message to the "Organizer" using the
"COMMENT" property. For example, if the user indicates tentative
acceptance and wants to let the "Organizer" know why, the reason can
be expressed in the "COMMENT" property value.
Silverberg, et. al. Standards Track [Page 21]

RFC 2446 iTIP November 1998
The "Organizer" may also receive a "REPLY" from one CU on behalf of
another. Like the scenario enumerated above for the "Organizer",
"Attendees" may have another CU respond on their behalf. This is done
using the "sent-by" parameter.
The optional properties listed in the table below (those listed as
"0+" or "0 or 1") MUST NOT be changed from those of the original
request. If property changes are desired the COUNTER message must be
used.
This method type is an iCalendar object that conforms to the
following property constraints:
Component/Property Presence
------------------- ----------------------------------------------
METHOD 1 MUST be "REPLY"
VEVENT 1+ All components MUST have the same UID
ATTENDEE 1 MUST be the address of the Attendee
replying.
DTSTAMP 1
ORGANIZER 1
RECURRENCE-ID 0 or 1 only if referring to an instance of a
recurring calendar component. Otherwise
it must NOT be present.
UID 1 MUST be the UID of the original REQUEST
SEQUENCE 0 or 1 MUST if non-zero, MUST be the sequence
number of the original REQUEST. MAY be
present if 0.
ATTACH 0+
CATEGORIES 0 or 1 This property may contain a list of values
CLASS 0 or 1
COMMENT 0 or 1
CONTACT 0+
CREATED 0 or 1
DESCRIPTION 0 or 1
DTEND 0 or 1 if present DURATION MUST NOT be present
DTSTART 0 or 1
DURATION 0 or 1 if present DTEND MUST NOT be present
EXDATE 0+
EXRULE 0+
GEO 0 or 1
LAST-MODIFIED 0 or 1
LOCATION 0 or 1
PRIORITY 0 or 1
RDATE 0+
RELATED-TO 0+
Silverberg, et. al. Standards Track [Page 22]

RFC 2446 iTIP November 1998
RESOURCES 0 or 1 This property MAY contain a list of values
REQUEST-STATUS 0+
RRULE 0+
STATUS 0 or 1
SUMMARY 0 or 1
TRANSP 0 or 1
URL 0 or 1
X-PROPERTY 0+
VTIMEZONE 0 or 1 MUST be present if any date/time refers
to a timezone
X-COMPONENT 0+
VALARM 0
VFREEBUSY 0
VJOURNAL 0
VTODO 0
3.2.4 ADD
The "ADD" method in a "VEVENT" calendar component is used to add one
or more instances to an existing "VEVENT". Unlike the "REQUEST"
method, when using issuing an "ADD" method, the "Organizer" does not
send the full "VEVENT" description; only the new instance(s). The
"ADD" method is especially useful if there are instance-specific
properties to be preserved in a recurring "VEVENT". For instance, an
"Organizer" may have originally scheduled a weekly Thursday meeting.
At some point, several instances changed. Location or start time may
have changed, or some instances may have unique "DESCRIPTION"
properties. The "ADD" method allows the "Organizer" to add new
instances to an existing event using a single ITIP message without
redefining the entire recurring pattern.
The "UID" must be that of the existing event. If the "UID" property
value in the "ADD" is not found on the recipient's calendar, then the
recipient SHOULD send a "REFRESH" to the "Organizer" in order to be
updated with the latest version of the "VEVENT". If an "Attendee"
implementation does not support the "ADD" method it should respond
with a "REQUEST-STATUS" value of 3.14 and ask for a "REFRESH".
This method type is an iCalendar object that conforms to the
following property constraints:
Silverberg, et. al. Standards Track [Page 23]

RFC 2446 iTIP November 19983.2.5 CANCEL
The "CANCEL" method in a "VEVENT" calendar component is used to send
a cancellation notice of an existing event request to the
"Attendees". The message is sent by the "Organizer" of the event. For
a recurring event, either the whole event or instances of an event
may be cancelled. To cancel the complete range of recurring event,
the "UID" property value for the event MUST be specified and a
"RECURRENCE-ID" MUST NOT be specified in the "CANCEL" method. In
order to cancel an individual instance of the event, the
"RECURRENCE-ID" property value for the event MUST be specified in the
"CANCEL" method.
There are two options for canceling a sequence of instances of a
recurring "VEVENT" calendar component:
(a) the "RECURRENCE-ID" property for an instance in the sequence MUST
be specified with the "RANGE" property parameter value of
THISANDPRIOR (or THISANDFUTURE) to indicate cancellation of the
specified "VEVENT" calendar component and all instances before
(or after); or
(b) individual recurrence instances may be cancelled by specifying
multiple "RECURRENCE-ID" properties corresponding to the
instances to be cancelled.
When a "VEVENT" is cancelled, the "SEQUENCE" property value MUST be
incremented.
This method type is an iCalendar object that conforms to the
following property constraints:
Component/Property Presence
------------------- ----------------------------------------------
METHOD 1 MUST be "CANCEL"
VEVENT 1+ All must have the same UID
ATTENDEE 0+ MUST include all "Attendees" being removed
the event. MUST include all "Attendees" if
the entire event is cancelled.
DTSTAMP 1
ORGANIZER 1
SEQUENCE 1
UID 1 MUST be the UID of the original REQUEST
COMMENT 0 or 1
ATTACH 0+
CATEGORIES 0 or 1 This property may contain a list of values
Silverberg, et. al. Standards Track [Page 25]

RFC 2446 iTIP November 1998
CLASS 0 or 1
CONTACT 0+
CREATED 0 or 1
DESCRIPTION 0 or 1
DTEND 0 or 1 if present DURATION MUST NOT be present
DTSTART 0 or 1
DURATION 0 or 1 if present DTEND MUST NOT be present
EXDATE 0+
EXRULE 0+
GEO 0 or 1
LAST-MODIFIED 0 or 1
LOCATION 0 or 1
PRIORITY 0 or 1
RDATE 0+
RECURRENCE-ID 0 or 1 MUST be present if referring to one or
more or more recurring instances.
Otherwise it MUST NOT be present
RELATED-TO 0+
RESOURCES 0 or 1
RRULE 0+
STATUS 0 or 1 MUST be set to CANCELLED. If uninviting
specific "Attendees" then MUST NOT be
included.
SUMMARY 0 or 1
TRANSP 0 or 1
URL 0 or 1
X-PROPERTY 0+
REQUEST-STATUS 0
VTIMEZONE 0+ MUST be present if any date/time refers to
a timezone
X-COMPONENT 0+
VTODO 0
VJOURNAL 0
VFREEBUSY 0
VALARM 0
3.2.6 REFRESH
The "REFRESH" method in a "VEVENT" calendar component is used by
"Attendees" of an existing event to request an updated description
from the event "Organizer". The "REFRESH" method must specify the
"UID" property of the event to update. A recurrence instance of an
event may be requested by specifying the "RECURRENCE-ID" property
corresponding to the associated event. The "Organizer" responds with
the latest description and version of the event.
Silverberg, et. al. Standards Track [Page 26]

RFC 2446 iTIP November 1998
VJOURNAL 0
VFREEBUSY 0
VTIMEZONE 0
VALARM 0
3.2.7 COUNTER
The "COUNTER" method for a "VEVENT" calendar component is used by an
"Attendee" of an existing event to submit to the "Organizer" a
counter proposal to the event description. The "Attendee" sends this
message to the "Organizer" of the event.
The counter proposal is an iCalendar object consisting of a VEVENT
calendar component describing the complete description of the
alternate event.
The "Organizer" rejects the counter proposal by sending the
"Attendee" a VEVENT "DECLINECOUNTER" method. The "Organizer" accepts
the counter proposal by rescheduling the event as described in
section 3.2.2.1 Rescheduling an Event.
This method type is an iCalendar object that conforms to the
following property constraints:
Component/Property Presence
------------------- ----------------------------------------------
METHOD 1 MUST be "COUNTER"
VEVENT 1
DTSTAMP 1
DTSTART 1
ORGANIZER 1 MUST be the "Organizer" of the original
event
SEQUENCE 1 MUST be present if value is greater than 0,
MAY be present if 0
SUMMARY 1 Can be null
UID 1 MUST be the UID associated with the REQUEST
being countered
ATTACH 0+
ATTENDEE 0+ Can also be used to propose other
"Attendees"
CATEGORIES 0 or 1 This property may contain a list of values
CLASS 0 or 1
COMMENT 0 or 1
CONTACT 0+
CREATED 0 or 1
DESCRIPTION 0 or 1
Silverberg, et. al. Standards Track [Page 28]

RFC 2446 iTIP November 1998
DTEND 0 or 1 if present DURATION MUST NOT be present
DURATION 0 or 1 if present DTEND MUST NOT be present
EXDATE 0+
EXRULE 0+
GEO 0 or 1
LAST-MODIFIED 0 or 1
LOCATION 0 or 1
PRIORITY 0 or 1
RDATE 0+
RECURRENCE-ID 0 or 1 MUST only if referring to an instance of a
recurring calendar component. Otherwise it
MUST NOT be present.
RELATED-TO 0+
REQUEST-STATUS 0+
RESOURCES 0 or 1 This property may contain a list of values
RRULE 0+
STATUS 0 or 1 Value must be one of CONFIRMED/TENATIVE/
CANCELLED
TRANSP 0 or 1
URL 0 or 1
X-PROPERTY 0+
VALARM 0+
VTIMEZONE 0+ MUST be present if any date/time refers to
a timezone
X-COMPONENT 0+
VTODO 0
VJOURNAL 0
VFREEBUSY 0
3.2.8 DECLINECOUNTER
The "DECLINECOUNTER" method in a "VEVENT" calendar component is used
by the "Organizer" of an event to reject a counter proposal submitted
by an "Attendee". The "Organizer" must send the "DECLINECOUNTER"
message to the "Attendee" that sent the "COUNTER" method to the
"Organizer".
This method type is an iCalendar object that conforms to the
following property constraints:
Silverberg, et. al. Standards Track [Page 29]

RFC 2446 iTIP November 19983.3 Methods For VFREEBUSY Components
This section defines the property set for the methods that are
applicable to the "VFREEBUSY" calendar component. Each of the methods
is defined using a restriction table.
This document only addresses the transfer of busy time information.
Applications desiring free time information MUST infer this from
available busy time information.
The busy time information within the iCalendar object MAY be grouped
into more than one "VFREEBUSY" calendar component. This capability
allows busy time periods to be grouped according to some common
periodicity, such as a calendar week, month, or year. In this case,
each "VFREEBUSY" calendar component MUST include the "ATTENDEE",
"DTSTART" and "DTEND" properties in order to specify the source of
the busy time information and the date and time interval over which
the busy time information covers.
The "FREEBUSY" property value MAY include a list of values, separated
by the COMMA character ([US-ASCII] decimal 44). Alternately, multiple
busy time periods MAY be specified with multiple instances of the
"FREEBUSY" property. Both forms MUST be supported by implementations
conforming to this document. Duplicate busy time periods SHOULD NOT
be specified in an iCalendar object. However, two different busy time
periods MAY overlap.
"FREEBUSY" properties should be sorted such that their values are in
ascending order, based on the start time, and then the end time, with
the earliest periods first. For example, today's busy time
information should appear after yesterday's busy time information.
And the busy time for this half-hour should appear after the busy
time for earlier today.
Since events may span a day boundary, free busy time period may also
span a day boundary. Individual "A" requests busy time from
individuals "B", "C" and "D". Individual "B" and "C" replies with
busy time data to individual "A". Individual "D" does not support
busy time requests and does not reply with any data. If the transport
binding supports exception messages, then individual "D" returns an
"unsupported capability" message to individual "A4.34.3".
The following summarizes the methods that are defined for the
"VFREEBUSY" calendar component.
Silverberg, et. al. Standards Track [Page 31]

RFC 2446 iTIP November 1998
|================|==================================================|
| Method | Description |
|================|==================================================|
| PUBLISH | Publish unsolicited busy time data. |
| REQUEST | Request busy time data. |
| REPLY | Reply to a busy time request. |
|================|==================================================|
3.3.1 PUBLISH
The "PUBLISH" method in a "VFREEBUSY" calendar component is used to
publish busy time data. The method may be sent from one CU to any
other. The purpose of the method is to provide a message for sending
unsolicited busy time data. That is, the busy time data is not being
sent as a "REPLY" to the receipt of a "REQUEST" method.
The "ATTENDEE" property must be specified in the busy time
information. The value is the CU address of the originator of the
busy time information.
This method type is an iCalendar object that conforms to the
following property constraints:
Component/Property Presence
------------------- ----------------------------------------------
METHOD 1 MUST be "PUBLISH"
VFREEBUSY 1+
DTSTAMP 1
DTSTART 1 DateTime values must be in UTC
DTEND 1 DateTime values must be in UTC
FREEBUSY 1+ MUST be BUSYTIME. Multiple instances are
allowed. Multiple instances must be sorted
in ascending order
ORGANIZER 1 MUST contain the address of originator of
busy time data.
COMMENT 0 or 1
CONTACT 0+
X-PROPERTY 0+
URL 0 or 1 Specifies busy time URL
ATTENDEE 0
DURATION 0
REQUEST-STATUS 0
UID 0
X-COMPONENT 0+
Silverberg, et. al. Standards Track [Page 32]

RFC 2446 iTIP November 1998
VEVENT 0
VTODO 0
VJOURNAL 0
VTIMEZONE 0
VALARM 0
3.3.2 REQUEST
The "REQUEST" method in a "VFREEBUSY" calendar component is used to
ask a "Calendar User" for their busy time information. The request
may be for a busy time information bounded by a specific date and
time interval.
This message only permits requests for busy time information. The
message is sent from a "Calendar User" requesting the busy time
information to one or more intended recipients.
If the originator of the "REQUEST" method is not authorized to make a
busy time request on the recipient's calendar system, then an
exception message SHOULD be returned in a "REPLY" method, but no busy
time data need be returned.
This method type is an iCalendar object that conforms to the
following property constraints:
Component/Property Presence
------------------- ----------------------------------------------
METHOD 1 MUST be "REQUEST"
VFREEBUSY 1
ATTENDEE 1+ contain the address of the calendar store
DTEND 1 DateTime values must be in UTC
DTSTAMP 1
DTSTART 1 DateTime values must be in UTC
ORGANIZER 1 MUST be the request originator's address
UID 1
COMMENT 0 or 1
CONTACT 0+
X-PROPERTY 0+
FREEBUSY 0
DURATION 0
REQUEST-STATUS 0
URL 0
X-COMPONENT 0+
VALARM 0
VEVENT 0
Silverberg, et. al. Standards Track [Page 33]

RFC 2446 iTIP November 1998
VTODO 0
VJOURNAL 0
VTIMEZONE 0
3.3.3 REPLY
The "REPLY" method in a "VFREEBUSY" calendar component is used to
respond to a busy time request. The method is sent by the recipient
of a busy time request to the originator of the request.
The "REPLY" method may also be used to respond to an unsuccessful
"REQUEST" method. Depending on the "REQUEST-STATUS" value, no busy
time information may be returned.
This method type is an iCalendar object that conforms to the
following property constraints:
Component/Property Presence
------------------- ----------------------------------------------
METHOD 1 MUST be "REPLY"
VFREEBUSY 1
ATTENDEE 1 (address of recipient replying)
DTSTAMP 1
DTEND 1 DateTime values must be in UTC
DTSTART 1 DateTime values must be in UTC
FREEBUSY 1+ (values MUST all be of the same data
type. Multiple instances are allowed.
Multiple instances MUST be sorted in
ascending order. Values MAY NOT overlap)
ORGANIZER 1 MUST be the request originator's address
UID 1
COMMENT 0 or 1
CONTACT 0+
REQUEST-STATUS 0+
URL 0 or 1 (specifies busy time URL)
X-PROPERTY 0+
DURATION 0
SEQUENCE 0
X-COMPONENT 0+
VALARM 0
VEVENT 0
VTODO 0
VJOURNAL 0
VTIMEZONE 0
Silverberg, et. al. Standards Track [Page 34]

RFC 2446 iTIP November 19983.4 Methods For VTODO Components
This section defines the property set for the methods that are
applicable to the "VTODO" calendar component. Each of the methods is
defined using a restriction table that specifies the property
constraints that define the particular method.
The following summarizes the methods that are defined for the "VTODO"
calendar component.
+================+==================================================+
| Method | Description |
|================+==================================================|
| PUBLISH | Post notification of a VTODO. Used primarily as |
| | a method of advertising the existence of a VTODO.|
| | |
| REQUEST | Assign a VTODO. This is an explicit assignment to|
| | one or more Calendar Users. The REQUEST method |
| | is also used to update or change an existing |
| | VTODO. Clients that cannot handle REQUEST MAY |
| | degrade the method to treat it as a PUBLISH. |
| | |
| REPLY | Reply to a VTODO request. Attendees MAY set |
| | PARTSTAT to ACCEPTED, DECLINED, TENTATIVE, |
| | DELEGATED, PARTIAL, and COMPLETED. |
| | |
| ADD | Add one or more instances to an existing to-do. |
| | |
| CANCEL | Cancel one or more instances of an existing |
| | to-do. |
| | |
| REFRESH | A request sent to a VTODO Organizer asking for |
| | the latest version of a VTODO. |
| | |
| COUNTER | Counter a REQUEST with an alternative proposal. |
| | |
| DECLINECOUNTER | Decline a counter proposal by an Attendee. |
+================+==================================================+
3.4.1 PUBLISH
The "PUBLISH" method in a "VTODO" calendar component has no
associated response. It is simply a posting of an iCalendar object
that maybe added to a calendar. It MUST have an "Organizer". It MUST
NOT have "Attendees". Its expected usage is for encapsulating an
arbitrary "VTODO" calendar component as an iCalendar object. The
"Organizer" MAY subsequently update (with another "PUBLISH" method),
add instances to (with an "ADD" method), or cancel (with a "CANCEL"
Silverberg, et. al. Standards Track [Page 35]

RFC 2446 iTIP November 1998
method) a previously published "VTODO" calendar component.
This method type is an iCalendar object that conforms to the
following property constraints:
Component/Property Presence
------------------- ----------------------------------------------
METHOD 1 MUST be "PUBLISH"
VTODO 1+
DTSTAMP 1
DTSTART 1
ORGANIZER 1
PRIORITY 1
SEQUENCE 0 or 1 MUST be present if value is greater than
0, MAY be present if 0
SUMMARY 1 Can be null.
UID 1
ATTACH 0+
CATEGORIES 0 or 1 This property may contain a list of values
CLASS 0 or 1
COMMENT 0 or 1
CONTACT 0+
CREATED 0 or 1
DESCRIPTION 0 or 1 Can be null
DUE 0 or 1 If present DURATION MUST NOT be present
DURATION 0 or 1 If present DUE MUST NOT be present
EXDATE 0+
EXRULE 0+
GEO 0 or 1
LAST-MODIFIED 0 or 1
LOCATION 0 or 1
PERCENT-COMPLETE 0 or 1
RDATE 0+
RECURRENCE-ID 0 or 1 MUST only if referring to an instance of a
recurring calendar component. Otherwise
it MUST NOT be present.
RELATED-TO 0+
RESOURCES 0 or 1 This property may contain a list of values
RRULE 0+
STATUS 0 or 1 MAY be one of COMPLETED/NEEDS ACTION/IN-
PROCESS/CANCELLED
URL 0 or 1
X-PROPERTY 0+
ATTENDEE 0
REQUEST-STATUS 0
Silverberg, et. al. Standards Track [Page 36]

RFC 2446 iTIP November 1998
VTIMEZONE 0+ MUST be present if any date/time refers to
a timezone
VALARM 0+
X-COMPONENT 0+
VFREEBUSY 0
VEVENT 0
VJOURNAL 0
3.4.2 REQUEST
The "REQUEST" method in a "VTODO" calendar component provides the
following scheduling functions:
. Assign a to-do to one or more "Calendar Users";
. Reschedule an existing to-do;
. Update the details of an existing to-do, without rescheduling
it;
. Update the completion status of "Attendees" of an existing
to-do, without rescheduling it;
. Reconfirm an existing to-do, without rescheduling it;
. Delegate/reassign an existing to-do to another "Calendar User".
The assigned "Calendar Users" are identified in the "VTODO" calendar
component by individual "ATTENDEE;ROLE=REQ-PARTICIPANT" property
value sequences.
The originator of a "REQUEST" is the "Organizer" of the to-do. The
recipient of a "REQUEST" is the "Calendar User" assigned the to-do.
The "Attendee" uses the "REPLY" method to convey their acceptance and
completion status to the "Organizer" of the "REQUEST".
The "UID", "SEQUENCE", and "DTSTAMP" properties are used to
distinguish the various uses of the "REQUEST" method. If the "UID"
property value in the "REQUEST" is not found on the recipient's
calendar, then the "REQUEST" is for a new to-do. If the "UID"
property value is found on the recipient's calendar, then the
"REQUEST" is a rescheduling, an update, or a reconfirm of the "VTODO"
calendar object.
If the "Organizer" of the "REQUEST" method is not authorized to make
a to-do request on the "Attendee's" calendar system, then an
exception is returned in the "REQUEST-STATUS" property of a
subsequent "REPLY" method, but no scheduling action is performed.
For the "REQUEST" method, multiple "VTODO" components in a single
iCalendar object are only permitted when for components with the same
"UID" property. That is, a series of recurring events may have
Silverberg, et. al. Standards Track [Page 37]

RFC 2446 iTIP November 1998
instance-specific information. In this case, multiple "VTODO"
components are needed to express the entire series.
This method type is an iCalendar object that conforms to the
following property constraints:
Component/Property Presence
------------------- ----------------------------------------------
METHOD 1 MUST be "REQUEST"
VTODO 1+ All components must have the same UID
ATTENDEE 1+
DTSTAMP 1
DTSTART 1
ORGANIZER 1
PRIORITY 1
SEQUENCE 0 or 1 MUST be present if value is greater than
0, MAY be present if 0
SUMMARY 1 Can be null.
UID 1
ATTACH 0+
CATEGORIES 0 or 1 This property may contain a list of
values
CLASS 0 or 1
COMMENT 0 or 1
CONTACT 0+
CREATED 0 or 1
DESCRIPTION 0 or 1 Can be null
DUE 0 or 1 If present DURATION MUST NOT be present
DURATION 0 or 1 If present DUE MUST NOT be present
EXDATE 0+
EXRULE 0+
GEO 0 or 1
LAST-MODIFIED 0 or 1
LOCATION 0 or 1
PERCENT-COMPLETE 0 or 1
RDATE 0+
RECURRENCE-ID 0 or 1 present if referring to an instance of a
recurring calendar component. Otherwise
it MUST NOT be present.
RELATED-TO 0+
RESOURCES 0 or 1 This property may contain a list of
values
RRULE 0+
STATUS 0 or 1 MAY be one of COMPLETED/NEEDS ACTION/IN-
PROCESS
URL 0 or 1
X-PROPERTY 0+
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RFC 2446 iTIP November 1998
REQUEST-STATUS 0
VALARM 0+
VTIMEZONE 0+ MUST be present if any date/time refers
to a timezone
X-COMPONENT 0+
VEVENT 0
VFREEBUSY 0
VJOURNAL 0
3.4.2.1 REQUEST for Rescheduling a VTODO
The "REQUEST" method may be used to reschedule a "VTODO" calendar
component.
Rescheduling a "VTODO" calendar component involves a change to the
existing "VTODO" calendar component in terms of its start or due time
or recurrence intervals and possibly the description. If the
recipient CUA of a "REQUEST" method finds that the "UID" property
value already exists on the calendar, but that the "SEQUENCE"
property value in the "REQUEST" is greater than the value for the
existing VTODO, then the "REQUEST" method describes a rescheduling of
the "VTODO" calendar component.
3.4.2.2 REQUEST for Update or Reconfirmation of a VTODO
The "REQUEST" method may be used to update or reconfirm a "VTODO"
calendar component. Reconfirmation is merely an update of "Attendee"
completion status or overall "VTODO" calendar component status.
An update to an existing "VTODO" calendar component does not involve
changes to the start or due time or recurrence intervals, nor
generally to the description for the "VTODO" calendar component. If
the recipient CUA of a "REQUEST" method finds that the "UID" property
value already exists on the calendar and that the "SEQUENCE" property
value in the "REQUEST" is the same as the value for the existing
event, then the "REQUEST" method describes an update of the "VTODO"
calendar component details, but not a rescheduling of the "VTODO"
calendar component.
The update "REQUEST" is the appropriate response to a "REFRESH"
method sent from an "Attendee" to the "Organizer" of a "VTODO"
calendar component.
Unsolicited "REQUEST" methods MAY be sent by the "Organizer" of a
"VTODO" calendar component. The unsolicited "REQUEST" methods are
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RFC 2446 iTIP November 1998
used to update the details of the "VTODO" (without rescheduling it or
updating the completion status of "Attendees") or the "VTODO"
calendar component itself (i.e., reconfirm the "VTODO").
3.4.2.3 REQUEST for Delegating a VTODO
The "REQUEST" method is also used to delegate or reassign ownership
of a "VTODO" calendar component to another "Calendar User". For
example, it may be used to delegate an "Attendee's" role (i.e.
"chair", or "participant") for a "VTODO" calendar component. The
"REQUEST" method is sent by one of the "Attendees" of an existing
"VTODO" calendar component to some other individual. An "Attendee" of
a "VTODO" calendar component MUST NOT delegate to the "Organizer" of
the event.
For the purposes of this description, the "Attendee" delegating the
"VTODO" calendar component is referred to as the "Delegator". The
"Attendee" receiving the delegation request is referred to as the
"Delegate".
The "Delegator" of a "VTODO" calendar component MUST forward the
existing "REQUEST" method for a "VTODO" calendar component to the
"Delegate". The "VTODO" calendar component description MUST include
the "Delegator's" up-to-date "VTODO" calendar component definition.
The "REQUEST" method MUST also include an "ATTENDEE" property with
the calendar address of the "Delegate". The "Delegator" MUST also
send a "REPLY" method back to the "Organizer" with the "Delegator's"
"Attendee" property "partstat" parameter value set to "DELEGATED". In
addition, the "delegated-to" parameter MUST be included with the
calendar address of the "Delegate". A response to the delegation
"REQUEST" is sent from the "Delegate" to the "Organizer" and
optionally, to the "Delegator". The "REPLY" method from the
"Delegate" SHOULD include the "ATTENDEE" property with their calendar
address and the "delegated-from" parameter with the value of the
"Delegator's" calendar address.
The delegation "REQUEST" method MUST assign a value for the "RSVP"
property parameter associated with the "Delegator's" "Attendee"
property to that of the "Delegate's" "ATTENDEE" property. For example
if the "Delegator's" "ATTENDEE" property specifies "RSVP=TRUE", then
the "Delegate's" "ATTENDEE" property MUST specify "RSVP=TRUE".
3.4.2.4 REQUEST Forwarded To An Uninvited Calendar User
An "Attendee" assigned a "VTODO" calendar component may send the
"VTODO" calendar component to another new CU, not previously
associated with the "VTODO" calendar component. The current
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RFC 2446 iTIP November 1998
"Attendee" assigned the "VTODO" calendar component does this by
forwarding the original "REQUEST" method to the new CU. The new CU
can send a "REPLY" to the "Organizer" of the "VTODO" calendar
component. The reply contains an "ATTENDEE" property for the new CU.
The "Organizer" ultimately decides whether or not the new CU becomes
part of the to-do and is not obligated to do anything with a "REPLY"
from a new (uninvited) CU. If the "Organizer" does not want the new
CU to be part of the to-do, the new "ATTENDEE" property is not added
to the "VTODO" calendar component. The "Organizer" MAY send the CU a
"CANCEL" message to indicate that they will not be added to the to-
do. If the "Organizer" decides to add the new CU, the new "ATTENDEE"
property is added to the "VTODO" calendar component. Furthermore, the
"Organizer" is free to change any "ATTENDEE" property parameter from
the values supplied by the new CU to something the "Organizer"
considers appropriate.
3.4.2.5 REQUEST Updated Attendee Status
An "Organizer" of a "VTODO" may request an updated status from one or
more "Attendees". The "Organizer" sends a "REQUEST" method to the
"Attendee" with the "ATTENDEE;RSVP=TRUE" property sequence. The
"SEQUENCE" property for the "VTODO" is not changed from its previous
value. A recipient determines that the only change in the "REQUEST"
is that their "RSVP" property parameter indicates a request for an
updated status. The recipient SHOULD respond with a "REPLY" method
indicating their current status with respect to the "REQUEST".
3.4.3 REPLY
The "REPLY" method in a "VTODO" calendar component is used to respond
(e.g., accept or decline) to a request or to reply to a delegation
request. It is also used by an "Attendee" to update their completion
status. When used to provide a delegation response, the "Delegator"
MUST include the calendar address of the "Delegate" in the
"delegated-to" parameter of the "Delegator's" "ATTENDEE" property.
The "Delegate" MUST include the calendar address of the "Delegator"
on the "delegated-from" parameter of the "Delegate's" "ATTENDEE"
property.
The "REPLY" method MAY also be used to respond to an unsuccessful
"VTODO" calendar component "REQUEST" method. Depending on the
"REQUEST-STATUS" value, no scheduling action may have been performed.
The "Organizer" of a "VTODO" calendar component MAY receive a "REPLY"
method from a "Calendar User" not in the original "REQUEST". For
example, a "REPLY" method MAY be received from a "Delegate" of a
"VTODO" calendar component. In addition, the "REPLY" method MAY be
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RFC 2446 iTIP November 1998
received from an unknown "Calendar User", having been forwarded the
"REQUEST" by an original "Attendee" of the "VTODO" calendar
component. This uninvited "Attendee" MAY be accepted, or the
"Organizer" MAY cancel the "VTODO" calendar component for the
uninvited "Attendee" by sending them a "CANCEL" method.
This method type is an iCalendar object that conforms to the
following property constraints:
Component/Property Presence
------------------- ---------------------------------------------
METHOD 1 MUST be "REPLY"
VTODO 1+ All component MUST have the same UID
ATTENDEE 1+
DTSTAMP 1
ORGANIZER 1
REQUEST-STATUS 1+
UID 1 MUST must be the address of the replying
attendee
ATTACH 0+
CATEGORIES 0 or 1 This property may contain a list of values
CLASS 0 or 1
COMMENT 0 or 1
CONTACT 0+
CREATED 0 or 1
DESCRIPTION 0 or 1
DTSTART 0 or 1
DUE 0 or 1 If present DURATION MUST NOT be present
DURATION 0 or 1 If present DUE MUST NOT be present
EXDATE 0+
EXRULE 0+
GEO 0 or 1
LAST-MODIFIED 0 or 1
LOCATION 0 or 1
PERCENT-COMPLETE 0 or 1
PRIORITY 0 or 1
RDATE 0+
RELATED-TO 0+
RESOURCES 0 or 1 This property may contain a list of values
RRULE 0+
RECURRENCE-ID 0 or 1 MUST only if referring to an instance of a
Recurring calendar component. Otherwise it
MUST NOT be present
SEQUENCE 0 or 1 MUST be the sequence number of
the original REQUEST if greater than 0.
MAY be present if 0.
STATUS 0 or 1
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RFC 2446 iTIP November 1998
SUMMARY 0 or 1 Can be null
URL 0 or 1
X-PROPERTY 0+
VTIMEZONE 0 or 1 MUST be present if any date/time refers to
a timezone
X-COMPONENT 0+
VALARM 0
VEVENT 0
VFREEBUSY 0
3.4.4 ADD
The "ADD" method in a "VTODO" calendar component is used to add one
or more instances to an existing to-do.
If the "UID" property value in the "ADD" is not found on the
recipient's calendar, then the recipient SHOULD send a "REFRESH" to
the "Organizer" in order to be updated with the latest version of the
"VTODO". If an "Attendee" implementation does not support the "ADD"
method it should respond with a "REQUEST-STATUS" value of 5.3 and ask
for a "REFRESH".
The "SEQUENCE" property value is incremented as the sequence of to-
dos has changed.
This method type is an iCalendar object that conforms to the
following property constraints:
Component/Property Presence
------------------- ----------------------------------------------
METHOD 1 MUST be "ADD"
VTODO 1
DTSTAMP 1
ORGANIZER 1
PRIORITY 1
SEQUENCE 1 MUST be greater than 0
SUMMARY 1 Can be null.
UID 1 MUST match that of the original to-do
ATTACH 0+
ATTENDEE 0+
CATEGORIES 0 or 1 This property may contain a list of
values
CLASS 0 or 1
COMMENT 0 or 1
CONTACT 0+
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RFC 2446 iTIP November 1998
CREATED 0 or 1
DESCRIPTION 0 or 1 Can be null
DTSTART 0 or 1
DUE 0 or 1 If present DURATION MUST NOT be present
DURATION 0 or 1 If present DUE MUST NOT be present
EXDATE 0+
EXRULE 0+
GEO 0 or 1
LAST-MODIFIED 0 or 1
LOCATION 0 or 1
PERCENT-COMPLETE 0 or 1
RDATE 0+
RELATED-TO 0+
RESOURCES 0 or 1 This property may contain a list of
values
RRULE 0+
STATUS 0 or 1 MAY be one of COMPLETED/NEEDS ACTION/IN-
PROCESS
URL 0 or 1
X-PROPERTY 0+
RECURRENCE-ID 0
REQUEST-STATUS 0
VALARM 0+
VTIMEZONE 0+ MUST be present if any date/time refers
to a timezone
X-COMPONENT 0+
VEVENT 0
VJOURNAL 0
VFREEBUSY 0
3.4.5 CANCEL
The "CANCEL" method in a "VTODO" calendar component is used to send a
cancellation notice of an existing "VTODO" calendar request to the
"Attendees". The message is sent by the "Organizer" of a "VTODO"
calendar component to the "Attendees" of the "VTODO" calendar
component. For a recurring "VTODO" calendar component, either the
whole "VTODO" calendar component or instances of a "VTODO" calendar
component may be cancelled. To cancel the complete range of a
recurring "VTODO" calendar component, the "UID" property value for
the "VTODO" calendar component MUST be specified and a "RECURRENCE-
ID" MUST NOT be specified in the "CANCEL" method. In order to cancel
an individual instance of a recurring "VTODO" calendar component, the
"RECURRENCE-ID" property value for the "VTODO" calendar component
MUST be specified in the "CANCEL" method.
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RFC 2446 iTIP November 1998
There are two options for canceling a sequence of instances of a
recurring "VTODO" calendar component:
(a) the "RECURRENCE-ID" property for an instance in the sequence MUST
be specified with the "RANGE" property parameter value of
THISANDPRIOR (or THISANDFUTURE) to indicate cancellation of the
specified "VTODO" calendar component and all instances before (or
after); or
(b) individual recurrence instances may be cancelled by specifying
multiple "RECURRENCE-ID" properties corresponding to the
instances to be cancelled.
When a "VTODO" is cancelled, the "SEQUENCE" property value MUST be
incremented.
This method type is an iCalendar object that conforms to the
following property constraints:
Component/Property Presence
------------------- ---------------------------------------------
METHOD 1 MUST be "CANCEL"
VTODO 1
ATTENDEE 0+ include all "Attendees" being removed from
the todo. MUST include all "Attendees" if
the entire todo is cancelled.
UID 1 MUST echo original UID
DTSTAMP 1
ORGANIZER 1
SEQUENCE 1
ATTACH 0+
CATEGORIES 0 or 1 This property MAY contain a list of values
CLASS 0 or 1
COMMENT 0 or 1
CONTACT 0+
CREATED 0 or 1
DESCRIPTION 0 or 1
DTSTART 0 or 1
DUE 0 or 1 If present DURATION MUST NOT be present
DURATION 0 or 1 If present DUE MUST NOT be present
EXDATE 0+
EXRULE 0+
GEO 0 or 1
LAST-MODIFIED 0 or 1
LOCATION 0 or 1
PERCENT-COMPLETE 0 or 1
RDATE 0+
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RFC 2446 iTIP November 1998
RECURRENCE-ID 0 or 1 MUST only if referring to one or more
instances of a recurring calendar
component. Otherwise it MUST NOT be
present.
RELATED-TO 0+
RESOURCES 0 or 1 This property MAY contain a list of values
RRULE 0+
PRIORITY 0 or 1
STATUS 0 or 1 If present it MUST be set to "CANCELLED".
MUST NOT be used if purpose is to remove
"ATTENDEES" rather than cancel the entire
VTODO.
URL 0 or 1
X-PROPERTY 0+
REQUEST-STATUS 0
VTIMEZONE 0 or 1 MUST be present if any date/time refers to
a timezone
X-COMPONENT 0+
VALARM 0
VEVENT 0
VFREEBUSY 0
3.4.6 REFRESH
The "REFRESH" method in a "VTODO" calendar component is used by
"Attendees" of an existing "VTODO" calendar component to request an
updated description from the "Organizer" of the "VTODO" calendar
component. The "Organizer" of the "VTODO" calendar component MAY use
this method to request an updated status from the "Attendees". The
"REFRESH" method MUST specify the "UID" property corresponding to the
"VTODO" calendar component needing update.
A refresh of a recurrence instance of a "VTODO" calendar component
may be requested by specifying the "RECURRENCE-ID" property
corresponding to the associated "VTODO" calendar component. The
"Organizer" responds with the latest description and rendition of the
"VTODO" calendar component. In most cases this will be a REQUEST
unless the "VTODO" has been cancelled, in which case the ORGANIZER
MUST send a "CANCEL". This method is intended to facilitate machine
processing of requests for updates to a "VTODO" calendar component.
This method type is an iCalendar object that conforms to the
following property constraints:
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RFC 2446 iTIP November 19983.4.7 COUNTER
The "COUNTER" method in a "VTODO" calendar component is used by an
"Attendee" of an existing "VTODO" calendar component to submit to the
"Organizer" a counter proposal for the "VTODO" calendar component.
The "Attendee" sends the message to the "Organizer" of the "VTODO"
calendar component.
The counter proposal is an iCalendar object consisting of a "VTODO"
calendar component describing the complete description of the
alternate "VTODO" calendar component.
The "Organizer" rejects the counter proposal by sending the
"Attendee" a "DECLINECOUNTER" method. The "Organizer" accepts the
counter proposal by sending all of the "Attendees" of the "VTODO"
calendar component a "REQUEST" method rescheduling the "VTODO"
calendar component. In the latter case, the "Organizer" SHOULD reset
the individual "RSVP" property parameter values to TRUE on each
"ATTENDEE" property; in order to force a response by the "Attendees".
This method type is an iCalendar object that conforms to the
following property constraints:
Component/Property Presence
------------------- ----------------------------------------------
METHOD 1 MUST be "COUNTER"
VTODO 1
ATTENDEE 1+
DTSTAMP 1
ORGANIZER 1
PRIORITY 1
SUMMARY 1 Can be null
UID 1
ATTACH 0+
CATEGORIES 0 or 1 This property MAY contain a list of values
CLASS 0 or 1
COMMENT 0 or 1
CONTACT 0+
CREATED 0 or 1
DESCRIPTION 0 or 1 Can be null
DTSTART 0 or 1
DUE 0 or 1 If present DURATION MUST NOT be present
DURATION 0 or 1 If present DUE MUST NOT be present
EXDATE 0+
EXRULE 0+
GEO 0 or 1
LAST-MODIFIED 0 or 1
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RFC 2446 iTIP November 1998
LOCATION 0 or 1
PERCENT-COMPLETE 0 or 1
RDATE 0+
RECURRENCE-ID 0 or 1 MUST only 3.5if referring to an instance of a
recurring calendar component. Otherwise it
MUST NOT be present.
RELATED-TO 0+
REQUEST-STATUS 0+
RESOURCES 0 or 1 This property MAY contain a list of values
RRULE 0 or 1
SEQUENCE 0 or 1 MUST echo the original SEQUENCE number.
MUST be present if non-zero. MAY be present
if zero.
STATUS 0 or 1 MAY be one of COMPLETED/NEEDS ACTION/IN-
PROCESS/CANCELLED
URL 0 or 1
X-PROPERTY 0+
VALARM 0+
VTIMEZONE 0 or 1 MUST be present if any date/time refers to
a timezone
X-COMPONENT 0+
VEVENT 0
VFREEBUSY 0
3.4.8 DECLINECOUNTER
The "DECLINECOUNTER" method in a "VTODO" calendar component is used
by an "Organizer" of "VTODO" calendar component to reject a counter
proposal offered by one of the "Attendees". The "Organizer" sends the
message to the "Attendee" that sent the "COUNTER" method to the
"Organizer".
This method type is an iCalendar object that conforms to the
following property constraints:
Component/Property Presence
------------------- ---------------------------------------------
METHOD 1 MUST be "DECLINECOUNTER"
VTODO 1
ATTENDEE 1+ MUST for all attendees
DTSTAMP 1
ORGANIZER 1
SEQUENCE 1 MUST echo the original SEQUENCE number
UID 1 MUST echo original UID
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RFC 2446 iTIP November 1998
ATTACH 0+
CATEGORIES 0 or 1 This property may contain a list of values
CLASS 0 or 1
COMMENT 0 or 1
CONTACT 0+
CREATED 0 or 1
DESCRIPTION 0 or 1
DTSTART 0 or 1
DUE 0 or 1 If present DURATION MUST NOT be present
DURATION 0 or 1 If present DUE MUST NOT be present
EXDATE 0+
EXRULE 0+
GEO 0 or 1
LAST-MODIFIED 0 or 1
LOCATION 0 or 1
PERCENT-COMPLETE 0 or 1
PRIORITY 0 or 1
RDATE 0+
RECURRENCE-ID 0 or 1 MUST only if referring to an instance of a
recurring calendar component. Otherwise
it MUST NOT be present.
RELATED-TO 0+
REQUEST-STATUS 0+
RESOURCES 0 or 1 This property MAY contain a list of values
RRULE 0+
STATUS 0 or 1 MAY be one of COMPLETED/NEEDS ACTION/IN-
PROCESS
URL 0 or 1
X-PROPERTY 0+
VTIMEZONE 0+ MUST be present if any date/time refers to
a timezone
X-COMPONENT 0+
VALARM 0
VEVENT 0
VFREEBUSY 0
3.5 Methods For VJOURNAL Components
This section defines the property set for the methods that are
applicable to the "VJOURNAL" calendar component.
The following summarizes the methods that are defined for the
"VJOURNAL" calendar component.
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RFC 2446 iTIP November 1998
+================+==================================================+
| Method | Description |
|================+==================================================|
| PUBLISH | Post a journal entry. Used primarily as a method |
| | of advertising the existence of a journal entry. |
| | |
| ADD | Add one or more instances to an existing journal |
| | entry. |
| | |
| CANCEL | Cancel one or more instances of an existing |
| | journal entry. |
+================+==================================================+
3.5.1 PUBLISH
The "PUBLISH" method in a "VJOURNAL" calendar component has no
associated response. It is simply a posting of an iCalendar object
that may be added to a calendar. It MUST have an "Organizer". It MUST
NOT have "Attendees". The expected usage is for encapsulating an
arbitrary journal entry as an iCalendar object. The "Organizer" MAY
subsequently update (with another "PUBLISH" method) or cancel (with a
"CANCEL" method) a previously published journal entry.
This method type is an iCalendar object that conforms to the
following property constraints:
Component/Property Presence
------------------- ----------------------------------------------
METHOD 1 MUST be "PUBLISH"
VJOURNAL 1+
DESCRIPTION 1 Can be null.
DTSTAMP 1
DTSTART 1
ORGANIZER 1
UID 1
ATTACH 0+
CATEGORIES 0 or 1 This property MAY contain a list of values
CLASS 0 or 1
COMMENT 0 or 1
CONTACT 0+
CREATED 0 or 1
EXDATE 0+
EXRULE 0+
LAST-MODIFIED 0 or 1
RDATE 0+
RECURRENCE-ID 0 or 1 MUST only if referring to an instance of a
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RFC 2446 iTIP November 1998
recurring calendar component. Otherwise
it MUST NOT be present.
RELATED-TO 0+
RRULE 0+
SEQUENCE 0 or 1 MUST echo the original SEQUENCE number.
MUST be present if non-zero. MAY be
present if zero.
STATUS 0 or 1 MAY be one of DRAFT/FINAL/CANCELLED
SUMMARY 0 or 1 Can be null
URL 0 or 1
X-PROPERTY 0+
ATTENDEE 0
VALARM 0+
VTIMEZONE 0+ MUST be present if any date/time refers to
a timezone
X-COMPONENT 0+
VEVENT 0
VFREEBUSY 0
VTODO 0
3.5.2 ADD
The "ADD" method in a "VJOURNAL" calendar component is used to add
one or more instances to an existing "VJOURNAL" entry. There is no
response to the "Organizer".
If the "UID" property value in the "ADD" is not found on the
recipient's calendar, then the recipient MAY treat the "ADD" as a
"PUBLISH".
This method type is an iCalendar object that conforms to the
following property constraints:
Component/Property Presence
------------------- ----------------------------------------------
METHOD 1 MUST be "ADD"
VJOURNAL 1
DESCRIPTION 1 Can be null.
DTSTAMP 1
DTSTART 1
ORGANIZER 1
SEQUENCE 1 MUST be greater than 0
UID 1 MUST match that of the original journal
ATTACH 0+
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RFC 2446 iTIP November 1998
CATEGORIES 0 or 1 This property MAY contain a list of values
CLASS 0 or 1
COMMENT 0 or 1
CONTACT 0+
CREATED 0 or 1
EXDATE 0+
EXRULE 0+
LAST-MODIFIED 0 or 1
RDATE 0+
RELATED-TO 0+
RRULE 0+
STATUS 0 or 1 MAY be one of DRAFT/FINAL/CANCELLED
SUMMARY 0 or 1 Can be null
URL 0 or 1
X-PROPERTY 0+
ATTENDEE 0
RECURRENCE-ID 0
VALARM 0+
VTIMEZONE 0 or 1 MUST be present if any date/time refers to
a timezone
X-COMPONENT 0+
VEVENT 0
VFREEBUSY 0
VTODO 0
3.5.3 CANCEL
The "CANCEL" method in a "VJOURNAL" calendar component is used to
send a cancellation notice of an existing journal entry. The message
is sent by the "Organizer" of a journal entry. For a recurring
journal entry, either the whole journal entry or instances of a
journal entry may be cancelled. To cancel the complete range of a
recurring journal entry, the "UID" property value for the journal
entry MUST be specified and a "RECURRENCE-ID" property MUST NOT be
specified in the "CANCEL" method. In order to cancel an individual
instance of the journal entry, the "RECURRENCE-ID" property value for
the journal entry MUST be specified in the "CANCEL" method.
There are two options for canceling a sequence of instances of a
recurring "VJOURNAL" calendar component:
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RFC 2446 iTIP November 1998
(a) the "RECURRENCE-ID" property for an instance in the sequence MUST
be specified with the "RANGE" property parameter value of
THISANDPRIOR (or THISANDFUTURE) to indicate cancellation of the
specified "VTODO" calendar component and all instances before (or
after); or
(b) individual recurrence instances may be cancelled by specifying
multiple "RECURRENCE-ID" properties corresponding to the
instances to be cancelled.
When a "VJOURNAL" is cancelled, the "SEQUENCE" property value MUST be
incremented.
This method type is an iCalendar object that conforms to the
following property constraints:
Component/Property Presence
------------------- ---------------------------------------------
METHOD 1 MUST be "CANCEL"
VJOURNAL 1+ All MUST have the same UID
DTSTAMP 1
ORGANIZER 1
SEQUENCE 1
UID 1 MUST be the UID of the original REQUEST
ATTACH 0+
ATTENDEE 0+
CATEGORIES 0 or 1 This property MAY contain a list of values
CLASS 0 or 1
COMMENT 0 or 1
CONTACT 0+
CREATED 0 or 1
DESCRIPTION 0 or 1
DTSTART 0 or 1
EXDATE 0+
EXRULE 0+
LAST-MODIFIED 0 or 1
RDATE 0+
RECURRENCE-ID 0 or 1 only if referring to an instance of a
recurring calendar component. Otherwise
it MUST NOT be present.
RELATED-TO 0+
RRULE 0+
STATUS 0 or 1 MAY be present, must be "CANCELLED" if
present
SUMMARY 0 or 1
URL 0 or 1
X-PROPERTY 0+
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RFC 2446 iTIP November 1998
Since implementations may elect to store recurring events as either a
single event object or a collection of discreet, related event
objects, the protocol is designed so that each recurring instance may
be both referenced and versioned. Hence, implementations that choose
to maintain per-instance properties (such as "ATTENDEE" property
"partstat" parameter) may do so. However, the protocol does not
require per-instance recognition unless the instance itself must be
renegotiated.
The scenarios for recurrence instance referencing are listed below.
For purposes of simplification a change to an event refers to a
"trigger property." That is, a property that has a substantive
effect on the meeting itself such as start time, location, due date
(for "VTODO" calendar component components) and possibly description.
"Organizer" initiated actions:
. "Organizer" deletes or changes a single instance of a recurring
event
. "Organizer" makes changes that affect all future instances
. "Organizer" makes changes that affect all previous instances
. "Organizer" deletes or modifies a previously changed instance
"Attendee" initiated actions:
. "Attendee" changes status for a particular recurrence instance
. "Attendee" sends Event-Counter for a particular recurrence
instance
An instance of a recurring event is assigned a unique identification,
"RECURRENCE-ID" property, when that instance is renegotiated.
Negotiation may be necessary when a substantive change to the event
or to-do has be made (such as changing the start time, end time, due
date or location). The "Organizer" can identify a specific recurrence
instance using the "RECURRENCE-ID" property. The property value is
equal to the date/time of the instance. If the "Organizer" wishes to
change the "DTSTART", the original "DTSTART" value is used for
"RECURRENCE-ID" property and the new "DTSTART" and "DTEND" values
reflect the change. Note that after the change has occurred, the
"RECURRENCE-ID" has changed to the new "DTSTART" value.
3.7.2 Attendee Property Considerations
The "ORGANIZER" property is required on published events, to-dos, and
journal entries for two reasons. First, only the "Organizer" is
allowed to update and redistribute an event or to-do component. It
follows that the "ORGANIZER" property MUST be present in the event,
to-do, or journal entry component so that the CUA has a basis for
Silverberg, et. al. Standards Track [Page 58]

RFC 2446 iTIP November 1998
authorizing an update. Second, it is prudent to provide a point of
contact for anyone who receives a published component in case of
problems.
There are valid [RFC-822] addresses that represent groups. Sending
email to such an address results in mail being sent to multiple
recipients. Such an address may be used as the value of an
"ATTENDEE" property. Thus, it is possible that the recipient of a
"REQUEST" does not appear explicitly in the list.
It is recommended that the general approach to finding a "Calendar
User" in an attendee list be as follows:
1. Search for the "Calendar User" in the attendee list where
"TYPE=INDIVIDUAL"
2. Failing (1) look for attendees where "TYPE=GROUP" or
'TYPE=UNKNOWN". The CUA then determines if the "Calendar User"
is a member of one of these groups. If so, the "REPLY" method
sent to the "Organizer" MUST contain a new "ATTENDEE" property in
which:
. the "type" property parameter is set to INDIVIDUAL
. the "member" property parameter is set to the name of the
group
3. Failing (2) the CUA MAY ignore or accept the request as the
"Calendar User" wishes.
3.7.3 X-Tokens
To make iCalendar objects extensible, new property types MAY be
inserted into components. These properties are called X-Tokens as
they are prefixed with "X-". A client is not required to make sense
of X-Tokens. Clients are not required to save X-Tokens or use them
in replies.
4 Examples4.1 Published Event Examples
In the calendaring and scheduling context, publication refers to the
one way transfer of event information. Consumers of published events
simply incorporate the event into a calendar. No reply is expected.
Individual "A" publishes an event. Individual "B" reads the event and
incorporates it into their calendar. Events are published in several
ways including: embedding the event as an object in a web page, e-
mailing the event to a distribution list, and posting the event to a
newsgroup.
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RFC 2446 iTIP November 1998
The table below illustrates the sequence of events between the
publisher and the consumers of a published event.
+-------------------------------------------------------------------+
| Action | "Organizer" |
+---------------------------------+---------------------------------+
| Publish an event | "A" sends or posts a PUBLISH |
| | message |
+---------------------------------+---------------------------------+
| "B" reads a published event | |
+---------------------------------+---------------------------------+
| Publish an updated event | "A" sends or posts a PUBLISH |
| | message |
+---------------------------------+---------------------------------+
| "B" reads the updated event | |
+---------------------------------+---------------------------------+
| Cancel a published event | "A" sends or posts a CANCEL |
| | message |
+---------------------------------+---------------------------------+
| "B" reads the canceled event | |
| publication | |
+---------------------------------+---------------------------------+
4.1.1 A Minimal Published Event
The iCalendar object below describes a single event that begins on
July 1, 1997 at 20:00 UTC. This event contains the minimum set of
properties for a "PUBLISH" for a "VEVENT" calendar component.
BEGIN:VCALENDAR
METHOD:PUBLISH
PRODID:-//ACME/DesktopCalendar//EN
VERSION:2.0
BEGIN:VEVENT
ORGANIZER:mailto:a@example.com
DTSTART:19970701T200000Z
DTSTAMP:19970611T190000Z
SUMMARY:ST. PAUL SAINTS -VS- DULUTH-SUPERIOR DUKES
UID:0981234-1234234-23@example.com
END:VEVENT
END:VCALENDAR
4.1.2 Changing A Published Event
The iCalendar object below describes an update to the event described
in 4.1.1, the time has been changed, an end time has been added, and
the sequence number has been adjusted.
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RFC 2446 iTIP November 1998
BEGIN:VCALENDAR
METHOD:PUBLISH
VERSION:2.0
PRODID:-//ACME/DesktopCalendar//EN
BEGIN:VEVENT
ORGANIZER:mailto:a@example.com
DTSTAMP:19970612T190000Z
DTSTART:19970701T210000Z
DTEND:19970701T230000Z
SEQUENCE:1
UID:0981234-1234234-23@example.com
SUMMARY:ST. PAUL SAINTS -VS- DULUTH-SUPERIOR DUKES
END:VEVENT
END:VCALENDAR
The "UID" property is used by the client to identify the event. The
"SEQUENCE" property indicates that this is a change to the event. The
event with a matching UID and sequence number 0 is superseded by this
event.
The "SEQUENCE" property provides a reliable way to distinguish
different versions of the same event. Each time an event is
published, its sequence number is incremented. If a client receives
an event with a sequence number 5 and finds it has the same event
with sequence number 2, the event SHOULD be updated. However, if the
client received an event with sequence number 2 and finds it already
has sequence number 5 of the same event, the event MUST NOT be
updated.
4.1.3 Canceling A Published Event
The iCalendar object below cancels the event described in 4.1.1. This
cancels the event with "SEQUENCE" property of 0, 1, and 2.
BEGIN:VCALENDAR
METHOD:CANCEL
VERSION:2.0
PRODID:-//ACME/DesktopCalendar//EN
BEGIN:VEVENT
ORGANIZER:mailto:a@example.com
COMMENT:DUKES forfeit the game
SEQUENCE:2
UID:0981234-1234234-23@example.com
DTSTAMP:19970613T190000Z
END:VEVENT
END:VCALENDAR
Silverberg, et. al. Standards Track [Page 61]

RFC 2446 iTIP November 1998
TRIGGER:-PT2H
ACTION:DISPLAY
DESCRIPTION:You should be leaving for the game now.
END:VALARM
BEGIN:VALARM
TRIGGER:-PT30M
ACTION:AUDIO
END:VALARM
END:VEVENT
END:VCALENDAR
The "RELATED-TO" field contains the "UID" property of a related
calendar event. The "SEQUENCE" property 3 indicates that this event
supersedes versions 0, 1, and 2.
4.1.5 Anniversaries or Events attached to entire days
This example demonstrates the use of the "value" parameter to tie a
"VEVENT" to day rather than a specific time.
BEGIN:VCALENDAR
PRODID:-//ACME/DesktopCalendar//EN
METHOD:PUBLISH
VERSION:2.0
BEGIN:VEVENT
ORGANIZER:mailto:a@example.com
DTSTAMP:19970614T190000Z
UID:0981234-1234234-23@example.com
DTSTART;VALUE=DATE:19970714
RRULE:FREQ=YEARLY;INTERVAL=1
SUMMARY: Bastille Day
END:VEVENT
END:VCALENDAR
4.2 Group Event Examples
Group events are distinguished from published events in that they
have "Attendees" and that there is interaction between the
"Attendees" and the "Organizer" with respect to the event. Individual
"A" requests a meeting between individuals "A", "B", "C" and "D".
Individual "B" confirms attendance to the meeting. Individual "C"
declines attendance. Individual "D" tentatively confirms attendance.
The following table illustrates the the message flow between these
individuals. A, the CU scheduling the meeting, is referenced as the
"Organizer".
Silverberg, et. al. Standards Track [Page 63]

RFC 2446 iTIP November 1998
BEGIN:VCALENDAR
PRODID:-//ACME/DesktopCalendar//EN
METHOD:DECLINECOUNTER
VERSION:2.0
BEGIN:VEVENT
ORGANIZER:Mailto:A@example.com
ATTENDEE;RSVP=TRUE;TYPE=INDIVIDUAL:Mailto:B@example.com
COMMENT:Sorry, I cannot change this meeting time
UID:calsrv.example.com-873970198738777@example.com
SEQUENCE:0
DTSTAMP:19970614T190000Z
END:VEVENT
END:VCALENDAR
4.2.5 Delegating an Event
When delegating an event request to another "Calendar User", the
"Delegator" must both update the "Organizer" with a "REPLY" and send
a request to the "Delegate". There is currently no protocol
limitation to delegation depth. It is possible for the original
delegate to delegate the meeting to someone else, and so on. When a
request is delegated from one CUA to another there are a number of
responsibilities required of the "Delegator". The "Delegator" MUST:
. Send a "REPLY" to the "Organizer" with the following updates:
. The "Delegator's" "ATTENDEE" property "partstat" parameter set
to "delegated" and the "delegated-to" parameter is set to the
address of the "Delegate"
. Add an additional "ATTENDEE" property for the "Delegate" with
the "delegated-from" property parameter set to the "Delegator"
. Indicate whether they want to continue to receive updates when
the "Organizer" sends out updated versions of the event.
Setting the "rsvp" property parameter to "TRUE" will cause the
updates to be sent, setting it to "FALSE" causes no further
updates to be sent. Note that in either case, if the "Delegate"
declines the invitation the "Delegator" will be notified.
. The "Delegator" MUST also send a copy of the original "REQUEST"
method to the "Delegate".
It is not required that the "Delegate" include the "Delegator" in
their "REPLY" method. However, it is strongly advised since this will
inform the "Delegator" whether the "Delegate" plans to attend the
meeting. [Editors note: How so?] If the "Delegate" declines the
meeting, the "Delegator" may elect to delegate the "REQUEST" to
another CUA. The process is the same.
Silverberg, et. al. Standards Track [Page 68]

RFC 2446 iTIP November 1998
BEGIN:VEVENT
ORGANIZER:MAILTO:A@Example.com
ATTENDEE;PARTSTAT=ACCEPTED;DELEGATED-
FROM="Mailto:C@example.com":Mailto:E@example.com
ATTENDEE;PARTSTAT=DELEGATED;
DELEGATED-TO="Mailto:E@example.com":Mailto:C@example.com
UID:calsrv.example.com-873970198738777@example.com
SEQUENCE:0
REQUEST-STATUS:2.0;Success
DTSTAMP:19970614T190000Z
END:VEVENT
END:VCALENDAR
4.2.7 Delegate Declines the Meeting
In this example the "Delegate" declines the meeting request and sets
the "ATTENDEE" property "partstat" parameter to "DECLINED". The
"Organizer" SHOULD resend the "REQUEST" to "C" with the "partstat"
parameter of the "Delegate" set to "declined". This lets the
"Delegator" know that the "Delegate" has declined and provides an
opportunity to the "Delegator" to either accept the request or
delegate it to another CU.
Response from "E" to "A" and "C". Note the use of the "COMMENT"
property "E" uses to indicate why the delegation was declined.
BEGIN:VCALENDAR
PRODID:-//ACME/DesktopCalendar//EN
METHOD:REPLY
VERSION:2.0
BEGIN:VEVENT
ORGANIZER:MAILTO:A@Example.com
ATTENDEE;PARTSTAT=DELEGATED;
DELEGATED-TO="Mailto:E@example.com":Mailto:C@example.com
ATTENDEE;PARTSTAT=DECLINED;
DELEGATED-FROM="Mailto:C@example.com":Mailto:E@example.com
COMMENT:Sorry, I will be out of town at that time.
UID:calsrv.example.com-873970198738777@example.com
SEQUENCE:0
REQUEST-STATUS:2.0;Success
DTSTAMP:19970614T190000Z
END:VEVENT
END:VCALENDAR
"A" resends the "REQUEST" method to "C". "A" may also wish to express
the fact that the item was delegated in the "COMMENT" property.
Silverberg, et. al. Standards Track [Page 71]

RFC 2446 iTIP November 1998
BEGIN:VCALENDAR
PRODID:-//ACME/DesktopCalendar//EN
METHOD:REQUEST
VERSION:2.0
BEGIN:VEVENT
ORGANIZER:MAILTO:A@Example.com
ATTENDEE;PARTSTAT=DECLINED;
DELEGATED-FROM="Mailto:C@example.com":Mailto:E@example.com
ATTENDEE;RSVP=TRUE:Mailto:C@example.com
UID:calsrv.example.com-873970198738777@example.com
SEQUENCE:0
SUMMARY:Phone Conference
DTSTART:19970701T180000Z
DTEND:19970701T200000Z
DTSTAMP:19970614T200000Z
COMMENT:DELEGATE (ATTENDEE Mailto:E@example.com) DECLINED YOUR
INVITATION
END:VEVENT
END:VCALENDAR
4.2.8 Forwarding an Event Request
The protocol does not prevent an "Attendee" from "forwarding" an
"VEVENT" calendar component to other "Calendar Users". Forwarding
differs from delegation in that the forwarded "Calendar User" (often
referred to as a "Party Crasher") does not replace the forwarding
"Calendar User". Implementations are not required to add the "Party
Crasher" to the "Attendee" list and hence there is no guarantee that
a "Party Crasher" will receive additional updates to the Event. The
forwarding "Calendar User" SHOULD NOT add the "Party Crasher" to the
attendee list. The "Organizer" MAY add the forwarded "Calendar User"
to the attendee list.
4.2.9 Cancel A Group Event
Individual "A" requests a meeting between individuals "A", "B", "C",
and "D". Individual "B" declines attendance to the meeting.
Individual "A" decides to cancel the meeting. The following table
illustrates the sequence of messages that would be exchanged between
these individuals.
Messages related to a previously canceled event ("SEQUENCE" property
value is less than the "SEQUENCE" property value of the "CANCEL"
message) MUST be ignored.
Silverberg, et. al. Standards Track [Page 72]

RFC 2446 iTIP November 19984.2.10 Removing Attendees
"A" wants to remove "B" from a meeting. This is done by sending a
"CANCEL" to "B" and removing "B" from the attendee list in the master
copy of the event.
+--------------------------------------------------------------------+
| Action | "Organizer" | "Attendee" |
+--------------------------------------------------------------------+
| Remove an "B" | "A" sends a CANCEL | |
| as an "Attendee" | message to "B" | |
+--------------------------------------------------------------------+
| Update the master | "A" sends the | |
| copy of the event | updated event to | |
| | the remaining | |
| | "Attendees" | |
+--------------------------------------------------------------------+
The original meeting includes "A", "B", "C", and "D". The example
below shows the "CANCEL" that "A" sends to "B". Note that in the
example below the "STATUS" property is omitted. This is used when the
meeting itself is cancelled and not when the intent is to remove an
"Attendee" from the Event.
BEGIN:VCALENDAR
PRODID:-//ACME/DesktopCalendar//EN
METHOD:CANCEL
VERSION:2.0
BEGIN:VEVENT
ORGANIZER:Mailto:A@example.com
ATTENDEE:mailto:B@example.com
COMMENT:You're off the hook for this meeting
UID:calsrv.example.com-873970198738777@example.com
DTSTAMP:19970613T193000Z
SEQUENCE:1
END:VEVENT
END:VCALENDAR
The updated master copy of the event is shown below. The "Organizer"
MAY resend the updated event to the remaining "Attendees". Note that
"B" has been removed.
BEGIN:VCALENDAR
PRODID:-//ACME/DesktopCalendar//EN
METHOD:REQUEST
VERSION:2.0
BEGIN:VEVENT
ORGANIZER:Mailto:A@example.com
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RFC 2446 iTIP November 1998
ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED:Mailto:A@example.com
ATTENDEE;TYPE=INDIVIDUAL:Mailto:C@example.com
ATTENDEE;TYPE=INDIVIDUAL:Mailto:D@example.com
ATTENDEE;TYPE=ROOM:CR_Big@example.com
ATTENDEE;ROLE=NON-PARTICIPANT;
RSVP=FALSE:Mailto:E@example.com
DTSTAMP:19970611T190000Z
DTSTART:19970701T200000Z
DTEND:19970701T203000Z
SUMMARY:Phone Conference
UID:calsrv.example.com-873970198738777@example.com
SEQUENCE:2
STATUS:CONFIRMED
END:VEVENT
END:VCALENDAR
4.2.11 Replacing the Organizer
The scenario for this example begins with "A" as the "Organizer" for
a recurring meeting with "B", "C", and "D". "A" receives a new job
offer in another country and drops out of touch. "A" left no
forwarding address or way to be reached. Using out-of-band
communication, the other "Attendees" eventually learn what has
happened and reach an agreement that "B" should become the new
"Organizer" for the meeting. To do this, "B" sends out a new version
of the event and the other "Attendees" agree to accept "B" as the new
"Organizer". "B" also removes "A" from the event.
When the "Organizer" is replaced, the "SEQUENCE" property value MUST
be incremented.
This is the message "B" sends to "C" and "D"
BEGIN:VCALENDAR
PRODID:-//ACME/DesktopCalendar//EN
METHOD:REQUEST
VERSION:2.0
BEGIN:VEVENT
ORGANIZER:Mailto:B@example.com
ATTENDEE;ROLE=CHAIR;STATUS=ACCEPTED:Mailto:B@example.com
ATTENDEE;TYPE=INDIVIDUAL:Mailto:C@example.com
ATTENDEE;TYPE=INDIVIDUAL:Mailto:D@example.com
DTSTAMP:19970611T190000Z
DTSTART:19970701T200000Z
DTEND:19970701T203000Z
RRULE:FREQ=WEEKLY
SUMMARY:Phone Conference
UID:123456@example.com
Silverberg, et. al. Standards Track [Page 75]

RFC 2446 iTIP November 1998
SEQUENCE:1
STATUS:CONFIRMED
END:VEVENT
END:VCALENDAR
4.3 Busy Time Examples
Busy time objects can be used in several ways. First, a CU may
request busy time from another CU for a specific range of time. That
request can be answered with a busy time Reply. Additionally, a CU
may simply publish their busy time for a given interval and point
other CUs to the published location. The following examples outline
both scenarios.
Individual "A" publishes busy time for one week.
BEGIN:VCALENDAR
PRODID:-//ACME/DesktopCalendar//EN
VERSION:2.0
METHOD:PUBLISH
BEGIN:VFREEBUSY
DTSTAMP:19980101T124100Z
ORGANIZER:MAILTO:A@Example.com
DTSTART:19980101T124200Z
DTEND:19980107T124200Z
FREEBUSY:19980101T180000Z/19980101T190000Z
FREEBUSY:19980103T020000Z/19980103T050000Z
FREEBUSY:19980107T020000Z/19980107T050000Z
FREEBUSY:19980113T000000Z/19980113T010000Z
FREEBUSY:19980115T190000Z/19980115T200000Z
FREEBUSY:19980115T220000Z/19980115T230000Z
FREEBUSY:19980116T013000Z/19980116T043000Z
END:VFREEBUSY
END:VCALENDAR
Individual "A" requests busy time from individuals "B", "C".
Individual "B" and "C" replies with busy time data to individual "A".
The following table illustrates the sequence of messages that would
be exchanged between these individuals.
Silverberg, et. al. Standards Track [Page 76]

RFC 2446 iTIP November 1998
UID:calsrv.example.com-873970198738777@example.com
SEQUENCE:0
STATUS:CONFIRMED
END:VEVENT
END:VCALENDAR
The first two components of this iCalendar object are the time zone
components. The "DTSTART" date coincides with the first instance of
the RRULE property.
The recurring meeting is defined in a particular time zone,
presumably that of the originator. The client for each "Attendee" has
the responsibility of determining the recurrence time in the
"Attendee's" time zone.
The repeating event starts on Tuesday, July 1, 1997 at 2:00pm PDT.
"Attendee" B@example.fr is in France where the local time on this
date is 9 hours ahead of PDT or 23:00. "Attendee" C@example.jp is in
Japan where local time is 8 hours ahead of UTC or Wednesday, July 2
at 06:00. The event repeats weekly on Tuesdays (in PST/PDT). The
"RRULE" property results in 20 instances. The last instance falls on
Tuesday, November 11, 1997 2:00pm PDT. The "RDATE" property adds
another instance: WED, 10-SEP-1997 2:00 PM PST.
There are two exceptions to this recurring appointment. The first one
is:
TUE, 09-SEP-1997 23:00 GMT
TUE, 09-SEP-1997 14:00 PDT
WED, 10-SEP-1997 06:00 JST
and the second is:
TUE, 28-OCT-1997 23:00 GMT
TUE, 28-OCT-1997 14:00 PST
WED, 29-OCT-1997 06:00 JST
4.4.2 Modify A Recurring Instance
In this example the "Organizer" issues a recurring meeting. Later the
"Organizer" changes an instance of the event by changing the
"DTSTART" property. Note the use of "RECURRENCE-ID" property and
"SEQUENCE" property in the second request.
Original Request:
BEGIN:VCALENDAR
METHOD:REQUEST
Silverberg, et. al. Standards Track [Page 79]

RFC 2446 iTIP November 1998
SUMMARY:IETF Calendaring Working Group Meeting
DTSTART:19970715T210000Z
DTEND:19970715T220000Z
LOCATION:Conference Call
DTSTAMP:19970629T093000Z
STATUS:CONFIRMED
END:VEVENT
END:VCALENDAR
4.4.7 Add A New Series of Instances To A Recurring Event
The scenario for this example involves an ongoing meeting, originally
set up to occur every Tuesday. The "Organizer" later decides that
the meetings need to be on Tuesdays and Thursdays, but does not want
to reschedule the entire meeting or lose any of the per-instance
information already collected.
The original event:
BEGIN:VCALENDAR
METHOD:REQUEST
PRODID:-//RDU Software//NONSGML HandCal//EN
VERSION:2.0
BEGIN:VEVENT
UID:123456789@host1.com
SEQUENCE:0
RRULE:WKST=SU;BYDAY=TU;FREQ=WEEKLY
ORGANIZER:Mailto:A@example.com
ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED:Mailto:A@example.com
ATTENDEE;RSVP=TRUE:Mailto:B@example.com
SUMMARY:Review Accounts
DTSTART:19980303T210000Z
DTEND:19980303T220000Z
LOCATION:The White Room
DTSTAMP:19980301T093000Z
STATUS:CONFIRMED
END:VEVENT
END:VCALENDAR
Assume that many other updates happen to this event and that a lot of
instance-specific information exists in the recurring series. The
"SEQUENCE" property value is 7 for the next update. Now the
"Organizer" wants to add Thursdays to the event:
BEGIN:VCALENDAR
METHOD:ADD
PRODID:-//RDU Software//NONSGML HandCal//EN
VERSION:2.0
Silverberg, et. al. Standards Track [Page 83]

RFC 2446 iTIP November 1998
BEGIN:VEVENT
UID:123456789@host1.com
SEQUENCE:7
RRULE:WKST=SU;BYDAY=TH;FREQ=WEEKLY
ORGANIZER:Mailto:A@example.com
ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED:Mailto:A@example.com
ATTENDEE;RSVP=TRUE:Mailto:B@example.com
SUMMARY:Review Accounts
DTSTART:19980303T210000Z
DTEND:19980303T220000Z
DTSTAMP:19980303T193000Z
LOCATION:The Usual conference room
STATUS:CONFIRMED
END:VEVENT
END:VCALENDAR
Alternatively, if the "Organizer" is not concerned with per-instance
updates, the entire event can be rescheduled using a "REQUEST". This
is done by using the "UID" of the event to reschedule and including
the modified "RRULE". Note, that since this is an entire rescheduling
of the event, any instance-specific information will be lost.
BEGIN:VCALENDAR
METHOD:REQUEST
PRODID:-//RDU Software//NONSGML HandCal//EN
VERSION:2.0
BEGIN:VEVENT
UID:123456789@host1.com
SEQUENCE:7
RRULE:WKST=SU;BYDAY=TU,TH;FREQ=WEEKLY
ORGANIZER:Mailto:A@example.com
ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED:Mailto:A@example.com
ATTENDEE;RSVP=TRUE:Mailto:B@example.com
SUMMARY:Review Accounts
DTSTART:19980303T210000Z
DTEND:19980303T220000Z
DTSTAMP:19980303T193000Z
LOCATION:The White Room
STATUS:CONFIRMED
END:VEVENT
END:VCALENDAR
The next series of examples illustrate how an "Organizer" would
respond to a "REFRESH" submitted by an "Attendee" after a series of
instance-specific modifications. To convey all instance-specific
changes, the "Organizer" must provide the latest event description
and the relevant instances. The first three examples show the history
including the initial "VEVENT" request and subsequent instance
Silverberg, et. al. Standards Track [Page 84]

RFC 2446 iTIP November 19984.5.7.1 Request for a Recurring VTODO
In this example "A" sends a recurring "VTODO" calendar component to
"B" and "D".
BEGIN:VCALENDAR
PRODID:-//ACME/DesktopCalendar//EN
METHOD:REQUEST
VERSION:2.0
BEGIN:VTODO
ORGANIZER:Mailto:A@example.com
ATTENDEE;ROLE=CHAIR:Mailto:A@example.com
ATTENDEE;RSVP=TRUE;TYPE=INDIVIDUAL:Mailto:B@example.com
ATTENDEE;RSVP=TRUE;TYPE=INDIVIDUAL:Mailto:D@example.com
RRULE:FREQ=MONTHLY;COUNT=10;BYDAY=1FR
DTSTART:19980101T100000-0700
DUE:19980103T100000-0700
SUMMARY:Send Status Reports to Area Managers
UID:calsrv.example.com-873970198738777-00@example.com
SEQUENCE:0
DTSTAMP:19970717T200000Z
STATUS:NEEDS ACTION
PRIORITY:1
END:VTODO
END:VCALENDAR
4.5.7.2 Calculating due dates in recurring VTODOs
The due date in a recurring "VTODO" calendar component is either a
fixed interval specified in the "REQUEST" method or specified using
the "RECURRENCE-ID" property. The former is calculated by applying
the difference between "DTSTART" and "DUE" properties and applying it
to each of the start of each recurring instance. Hence, if the
initial "VTODO" calendar component specifies a "DTSTART" property
value of "19970701T190000Z" and a "DUE" property value of
"19970801T190000Z" the interval of one day which is applied to each
recurring instance of the "VTODO" calendar component to determine the
"DUE" date of the instance.
4.5.7.3 Replying to an instance of a recurring VTODO
In this example "B" updates "A" on a single instance of the "VTODO"
calendar component.
BEGIN:VCALENDAR
PRODID:-//ACME/DesktopCalendar//EN
METHOD:REPLY
VERSION:2.0
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RFC 2446 iTIP November 1998
ATTENDEE:Mailto:D@example.com
UID: guid-1-12345@host1.com
DTSTAMP:19970603T094000
END:VEVENT
END:VCALENDAR
4.7.2 Bad RECURRENCE-ID
Component instances are identified by the combination of "UID",
"RECURRENCE-ID", and "SEQUENCE". When an "Organizer" sends a request
to an "Attendee", there are three cases in which an instance cannot
be found. They are:
1. The component with the referenced "UID" and "RECURRENCE-ID" has
been found but the "SEQUENCE" number in the calendar store does
not match that of the ITIP message.
2. The component with the referenced "UID" has been found, the
"SEQUENCE" numbers match, but the "RECURRENCE-ID" cannot be
found.
3. The "UID" and "SEQUENCE" numbers are found but the CUA does not
support recurrences.
In case (1), two things can happen. If the "SEQUENCE" number of the
"Attendee's" instance is larger than that in the "Organizer's"
message then the "Attendee" is receiving an out-of-sequence message
and MUST ignore it. If the "SEQUENCE" number of the "Attendee's"
instance is smaller, then the "Organizer" is sending out a newer
version of the component and the "Attendee's" version needs to be
updated. Since one or more updates have been missed, the "Attendee"
SHOULD send a "REFRESH" message to the "Organizer" to get an updated
version of the event.
In case (2), something has gone wrong. Both the "Organizer" and the
"Attendee" should have the same instances, but the "Attendee" does
not have the referenced instance. In this case the "Attendee" SHOULD
send a "REFRESH" to the "Organizer" to get an updated version of the
event.
In case (3), the limitations of the "Attendee's" CUA makes it
impossible to match an instance other than the single instance
scheduled. In this case, the "Attendee" need not send a "REFRESH" to
the "Organizer".
The example below shows a sequence in which an "Attendee" sends a
"REFRESH" to the "Organizer".
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RFC 2446 iTIP November 1998
missed at least one update and needs a new copy of the event. "B"
requests the latest copy of the event with the following refresh
message:
BEGIN:VCALENDAR
PRODID:-//RDU Software//NONSGML HandCal//EN
METHOD:REFRESH
VERSION:2.0
BEGIN:VEVENT
ORGANIZER:Mailto:A@example.com
ATTENDEE:Mailto:B@example.com
UID:acme-12345@host1.com
DTSTAMP:19970603T094000
END:VEVENT
END:VCALENDAR
5 Application Protocol Fallbacks5.1 Partial Implementation
Applications that support this memo are not required to support the
entire protocol. The following describes how methods and properties
SHOULD "fallback" in applications that do not support the complete
protocol. If a method or property is not addressed in this section,
it may be ignored.
5.1.1 Event-Related Fallbacks
Method Fallback
-------------- -----------------------------------------------------
PUBLISH Required
REQUEST PUBLISH
REPLY Required
ADD Required
CANCEL Required
REFRESH Required
COUNTER Reply with Not Supported
DECLINECOUNTER Required if EVENT-COUNTER is implemented; otherwise
reply with Not Supported
iCalendar
Property Fallback
-------------- -----------------------------------------------------
CALSCALE Ignore; assume GREGORIAN
PRODID Ignore
METHOD Required as described in the Method list above
VERSION Ignore
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RFC 2446 iTIP November 1998
Component
Property Fallback
-------------- -----------------------------------------------------
ATTACH Ignore
ATTENDEE Required if JOURNAL-REQUEST is implemented; otherwise
ignore
CATEGORIES Ignore
CLASS Ignore
COMMENT Ignore
CONTACT Ignore
CREATED Ignore
DESCRIPTION Required
DTSTAMP Required
DTSTART Required
EXDATE Ignore
EXRULE Ignore Reply with Not Supported. If implemented,
VTIMEZONE MUST also be implemented.
LAST-MODIFIED Ignore
ORGANIZER Ignore
RECURRENCE-ID Ignore
RELATED-TO Ignore
RDATE Ignore.
RRULE Ignore. The first instance occurs on the DTSTART
property. If implemented, VTIMEZONE MUST also be
implemented.
SEQUENCE Required
STATUS Ignore
SUMMARY Required
URL Ignore
UID Required
X- Ignore
5.2 Latency Issues
With a store-and-forward transport, it is possible for events to
arrive out of sequence. That is, a "CANCEL" method may be received
prior to receiving the associated "REQUEST" for the calendar
component. This section discusses a few of these scenarios.
5.2.1 Cancellation of an Unknown Calendar Component.
When a "CANCEL" method is received before the original "REQUEST"
method the calendar will be unable to correlate the "UID" property of
the cancellation with an existing calendar component. It is suggested
that messages that can not be correlated that also contain non-zero
sequence numbers be held and not discarded. Implementations MAY age
them out if no other messages arrive with the same "UID" property
value and a lower sequence number.
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RFC 2446 iTIP November 19985.2.2 Unexpected Reply from an Unknown Delegate
When an "Attendee" delegates an item to another CU they MUST send a
"REPLY" method to the "Organizer" using the "ATTENDEE" properties to
indicate that the request was delegated and to whom. Hence, it is
possible for an "Organizer" to receive an "REPLY" from a CU not
listed as one of the original "Attendees". The resolution is left to
the implementation but it is expected that the calendaring software
will either accept the reply or hold it until the related "REPLY"
method is received from the "Delegator". If the version of the
"REPLY" method is out of date the "Organizer" SHOULD treat the
message as a "REFRESH" message and update the delegate with the
correct version.
5.3 Sequence Number
Under some conditions, a CUA may receive requests and replies with
the same "SEQUENCE" property value. The "DTSTAMP" property is
utilized as a tie-breaker when two items with the same "SEQUENCE"
property value are evaluated.
6 Security Considerations
ITIP is an abstract transport protocol which will be bound to a
real-time transport, a store-and-forward transport, and perhaps other
transports. The transport protocol will be responsible for providing
facilities for authentication and encryption using standard Internet
mechanisms that are mutually understood between the sender and
receiver.
6.1 Security Threats6.1.1 Spoofing the "Organizer"
In iTIP, the "Organizer" (or someone working on the "Organizer's"
behalf) is the only person authorized to make changes to an existing
"VEVENT", "VTODO", "VJOURNAL" calendar component and republish it or
redistribute updates to the "Attendees". An iCalendar object that
maliciously changes or cancels an existing "VEVENT", "VTODO" or
"VJOURNAL" calendar component may be constructed by someone other
than the "Organizer" and republished or sent to the "Attendees".
6.1.2 Spoofing the "Attendee"
In iTIP, an "Attendee" of a "VEVENT" or "VTODO" calendar component
(or someone working on the "Attendee's" behalf) is the only person
authorized to update any parameter associated with their "ATTENDEE"
property and send it to the "Organizer". An iCalendar object that
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RFC 2446 iTIP November 1998
maliciously changes the "ATTENDEE" parameters may be constructed by
someone other than the real "Attendee" and sent to the "Organizer".
6.1.3 Unauthorized Replacement of the Organizer
There will be circumstances when "Attendees" of an event or to-do
decide, using out-of-band mechanisms, that the "Organizer" must be
replaced. When the new "Organizer" sends out the updated "VEVENT" or
"VTODO" the "Attendee's" CUA will detect that the "Organizer" has
been changed, but it has no way of knowing whether or not the change
was mutually agreed upon.
6.1.4 Eavesdropping
The iCalendar object is constructed with human-readable clear text.
Any information contained in an iCalendar object may be read and/or
changed by unauthorized persons while the object is in transit.
6.1.5 Flooding a Calendar
Implementations MAY provide a means to automatically incorporate
"REQUEST" methods into a calendar. This presents the opportunity for
a calendar to be flooded with requests, which effectively block all
the calendar's free time.
6.1.6 Procedural Alarms
The "REQUEST" methods for "VEVENT" and "VTODO" calendar components
MAY contain "VALARM" calendar components. The "VALARM" calendar
component may be of type "PROCEDURE" and MAY have an attachment
containing an executable program. Implementations that incorporate
these types of alarms are subject to any virus or malicious attack
that may occur as a result of executing the attachment.
6.1.7 Unauthorized REFRESH Requests
It is possible for an "Organizer" to receive a "REFRESH" request from
someone who is not an "Attendee" of an event or to-do. Only
"Attendee's" of an event or to-do are authorized to receive replies
to "REFRESH" requests. Replying to such requests to anyone who is not
an "Attendee" may be a security problem.
6.2 Recommendations
For an application where the information is sensitive or critical and
the network is subject is subject to a high probability of attack,
iTIP transactions SHOULD be encrypted. This may be accomplished using
public key technology, specifically Security Multiparts for MIME
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RFC 2446 iTIP November 1998
[RFC-1847] in the iTIP transport binding. This helps mitigate the
threats of spoofing, eavesdropping and malicious changes in transit.
6.2.1 Use of [RFC-1847] to secure iTIP transactions
iTIP transport bindings MUST provide a mechanism based on Security
Multiparts for MIME [RFC-1847] to enable authentication of the
sender's identity, and privacy and integrity of the data being
transmitted. This allows the receiver of a signed iCalendar object to
verify the identity of the sender. This sender may then be correlated
to an "ATTENDEE" property in the iCalendar object. If the correlation
is made and the sender is authorized to make the requested change or
update then the operation may proceed. It also allows the message to
be encrypted to prevent unauthorized reading of the message contents
in transit. iTIP transport binding documents describe this process in
detail.
Implementations MAY provide controls for users to disable this
capability.
6.2.2 Implementation Controls
The threat of unauthorized replacement of the "Organizer" SHOULD be
mitigated by a calendar system that uses this protocol by providing
controls or alerts that make "Calendar Users" aware of such
"Organizer" changes and allowing them to decide whether or not the
request should be honored.
The threat of flooding a calendar SHOULD be mitigated by a calendar
system that uses this protocol by providing controls that may be used
to limit the acceptable sources for iTIP transactions, and perhaps
the size of messages and volume of traffic, by source.
The threat of malicious procedural alarms SHOULD be mitigated by a
calendar system that uses this protocol by providing controls that
may be used to disallow procedural alarms in iTIP transactions and/or
remove all alarms from the object before delivery to the recipient.
The threat of unauthorized "REFRESH" requests SHOULD be mitigated by
a calendar system that uses this protocol by providing controls or
alerts that allow "Calendar User" to decide whether or not the
request should be honored. An implementation MAY decide to maintain,
for audit or historical purposes, "Calendar Users" who were part of
an attendee list and who were subsequently uninvited. Similar
controls or alerts should be provided when a "REFRESH" request is
received from these "Calendar Users" as well.
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RFC 2446 iTIP November 199810. Full Copyright Statement
Copyright (C) The Internet Society (1998). All Rights Reserved.
This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this paragraph are
included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of
developing Internet standards in which case the procedures for
copyrights defined in the Internet Standards process must be
followed, or as required to translate it into languages other than
English.
The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns.
This document and the information contained herein is provided on an
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Silverberg, et. al. Standards Track [Page 109]